Rather than relying on always having a full cloned repository when
building, add fallbacks which work for trees with constrained (such
as shallow-cloned trees), or no, history. When the tagged commit is
reachable, use git describe, else rely on the version string in
configure since that's required to always be there regardless of
distribution mode. If we have git tree then include the HEAD sha1
as well.

While there, clean up versioning to more clearly separate us from
upstream.

Summary:
* Properly propagate the C++ compiler from autoconf
* Disable aggressive loop optimizations in GCC 4.8+

This commit is in the spirit of postgres/postgres@105f3ef4 , but done
for C++ code so that the GPORCA translator can properly build when the
compiler is GCC 4.8+

Fixes greenplum-db/gpdb#1186 .

TL;DR, here is the additional context on what specific to GPORCA translator:

GCC 6.2.0 compiler (which is required for codegen) got aggressive loop optimization to remove loop when enumerating variable length array.

In code `CTranslatorRelcacheToDXL.cpp`, we have a loop to enumerate all
the attributes of an index:

```
INT iAttno = pgIndex->indkey.values[ul];
```

Where `values[ul]` is of following data structure:

```
typedef struct
{
...
	int2		values[1];		/* VARIABLE LENGTH ARRAY */
} int2vector;					/* VARIABLE LENGTH STRUCT */
```

This is standard way of dealing with variable length array in Postgres. However, optimizer
thinking there is only 1 element, hence removed the loop.

This caused wrong result when using GPDB with GPORCA. The repro is
```
-- multi-column index
create table index_test (a int, b int, c int, d int, e int,
  constraint index_test_pkey PRIMARY KEY (a, b, c, d));

insert into index_test select i,i%2,i%3,i%4,i%5 from generate_series(1,100) i;

-- expecting using index scan with index cond: c=5
explain select * from index_test where c = 5;
```

When compile with GCC 6.2.0, the `index scan` is not selected, but a `table scan` is chosen
instead. The root cause is the compiler removed the loop, and only keep the first column.

The fix is to add $CXXFLAG auto detection to add the
`-fno-aggressive-loop-optimizations` for $CXX compilers if that version of compiler supporting
such optimization. Hence to avoid having the above issue for gpopt component.

This attempts to clean up the autoconf script a bit and follow the
upstream division of generic code in config/ with the actual lookup
configuration in configure.in. Also updated our installation to rely
on a more modern version of autoconf by backporting parts of upstream
commit 7cc514ac. This commit consist of:

  * Decouple --enable-codegen and --with-codegen-prefix to not
    silently ignore prefixes if the enable flag isn't passed.
	Emit a warning if configuring prefixes without codegen. Also
	moves --with-codegen-prefix to require an argument since
	--with-codegen-prefix without an argument is likely to hide
	either a scripting bug or a misunderstanding from the user
  * Move program checks for cmake and apr-1-config to programs.m4
    and allow for path overrides and ensure to use the resolved
	path when invoking cmake for --enable-codegen
  * Propagate the apr-1-config flags and objects to where used via
    Makefile.global rather than performing another lookup
  * Remove check for unused arguments since autoconf does that
    automatically since 2.63
  * Remove backported fseeko handling since that isn't relevant
    for modern autoconf versions
  * Minor help output tidying and spelling fixes

Since we discover the apr-1-config binary during the configure stage
we might as well simplify the gpfdist Makefile by using it during
building. Also renames the APR_CONFIG variable to avoid colliding
with $APR_CONFIG using the gpAux makefile.

Squashed commit of the following:

commit db752c0c916f36479b0c5049c671538565294c25
Author: Nikos Armenatzoglou <narmenatzoglou@gmail.com>
Date:   Thu Mar 24 14:01:38 2016 -0700

    Adding check to avoid unit test failures when sizeof(long) = 8

commit 1c39c58279cf73af92811ed1b2e6f2bc22d01414
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Thu Mar 17 19:42:47 2016 +0000

    --with-codegen-prefix instead of CMAKE_PREFIX_PATH

commit 77978e92444580bc4e84dc3f6b3e366a09e92dba
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Thu Mar 10 14:57:48 2016 +0000

    Make codegen work with GPDB build system and other minor fixes

      * Update CMakeLists to build SUBSYS.o
      * Update CMakeLists to build release build by default
      * Update CMakeLists to add tests in a loop.
      * Add codegen and cmake specific .gitignore
      * Update license and READMEs
      * Move codegen utils related header files back into src/backend/codegen/include/codegen
Signed-off-by: NNikos Armenatzoglou <nikos.armenatzoglou@gmail.com>

commit 1b61c12f4eb082f49a66c28957c22810e98a5074
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Wed Mar 16 21:06:28 2016 +0000

    Remove codegen specific gtest source tree and use the one in gpAux.
Signed-off-by: NNikos Armenatzoglou <nikos.armenatzoglou@gmail.com>

commit 13bb2dcf3465be0ef240e316a149b2d8a125a9e9
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Thu Mar 10 02:51:29 2016 +0000

    Set up GPDB to use codegen utilities

      * Move in codegen utility source and include files to GPDB specific locations.
      * Configure codegen with --enable-codegen and use gpcodegen namespace
Signed-off-by: NNikos Armenatzoglou <nikos.armenatzoglou@gmail.com>

commit 9a4e40f931f71cb7a82e15b51745944116bc10ab
Author: Craig Chasseur <spoonboy42@gmail.com>
Date:   Mon Nov 2 09:10:37 2015 -0800

    Introduce codegen utilties into GPDB.

    Support library for integrating LLVM code-generation and runtime
    compilation with Clang in a larger codebase.
Signed-off-by: NNikos Armenatzoglou <nikos.armenatzoglou@gmail.com>

This adds a new switch to autoconf, --enable-mapreduce, to connect
the GPMapreduce extension to the build. If set to on the mapreduce
extension in gpAux/extensions will be built and installed.  As a
side effect this will properly clean and distclean for gpfdist in
gpAux/extensions as well. Autoconf checks for libyaml since it's
a depedency for GPMapreduce.

This is the first stab at gpmapreduce, once in we can start moving
gpmapreduce back into src/bin and move the mapreduce test suite in
under gpAux/extensions.

We no longer support --with-java, --enable-email or --enable-nls
so remove from definitions. Rather than removing enable_nls comment
it out and make comment match whats in configure.in though.

As gpfdist will now be part of the gpdb build by default, we may just
treat it as part of gpdb core.
* Integrate gpfdist configure file to the top level configure and
  changed necessary files to accomadate the changes.
* Modify travis.yml for gpfdist structural changes
* Update gpfdist.c to use GP_VERSION from pg_config.h

Fix warning issues from transform.c
* There were many prototype warnings that was being mentioned.
  Added a headerfile for missing prototype warnings, also included the
  structs into the headerfile.

Replace src/port/glob.c
* src/port/glob.c is dead code at the moment and can be safely replaced by
  the windows changes from gpfdist/port

Check for libyaml:
* disable transformations for gpfdist if not found.

* Add configuration option for gpfdist
use --disable-gpfdist to turn off gpfdist build

Enable to run extension regression tests from top level makefile

* Add installcheck gpfdist into extensions
* Add check for enterprise targeted builds
* Pass apr config to gpfdist
* Add JAVA_HOME check

Authors:
Marbin Tan and Shujie Shang

This patch merges the PostgreSQL 9.5 implementation of SSE4.2 into GPDB.
The SSE4.2 implementation was lifted right out of PostgreSQL without
change to make merging later PostgreSQL releases easier.

Update win32 configuration to support SSE4.2 runtime checks

This change was pulled from "src/include/pg_config.h.win32" from the
commits below.

configure.in changes, determining if cpu instruction for perfomring runtime
checks are availible, and moving some of the code to port SSE4.2 came from the
following PostgreSQL commits:

commit 3dc2d62d
Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:   Tue Apr 14 17:05:03 2015 +0300

    Use Intel SSE 4.2 CRC instructions where available.

    Modern x86 and x86-64 processors with SSE 4.2 support have special
    instructions, crc32b and crc32q, for calculating CRC-32C. They greatly
    speed up CRC calculation.

    Whether the instructions can be used or not depends on the compiler and the
    target architecture. If generation of SSE 4.2 instructions is allowed for
    the target (-msse4.2 flag on gcc and clang), use them. If they are not
    allowed by default, but the compiler supports the -msse4.2 flag to enable
    them, compile just the CRC-32C function with -msse4.2 flag, and check at
    runtime whether the processor we're running on supports it. If it doesn't,
    fall back to the slicing-by-8 algorithm. (With the common defaults on
    current operating systems, the runtime-check variant is what you get in
    practice.)

    Abhijit Menon-Sen, heavily modified by me, reviewed by Andres Freund.

commit b4eb2d16
Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:   Tue Apr 14 19:56:00 2015 +0300
	On gcc and clang, the _mm_crc32_u8 and _mm_crc32_u64 intrinsics are not
	defined at all, when not building with -msse4.2. But on icc, they are.
	So we cannot assume that if those intrinsics are defined, we can always use
	them safely, we might still need the runtime check.

	To fix, check if the __SSE_4_2__ preprocessor symbol is defined. That's
	supposed to be defined only when the compiler is targeting a processor that
	has SSE 4.2 support.

	Per buildfarm members fulmar and okapi.

It's important to pay attention to compiler warnings, but -Werror isn't
buying us much at the moment. Firstly, there are a lot of warnings on modern
versions of gcc. I have to pass: "-Wno-error=unused-but-set-variable
-Wno-error=enum-compare -Wno-error=address -Wno-error=maybe-uninitialized"
to make it compile. More important than erroring out on warnings is to make
sure there are no warnings to begin with. Once we get to that state, any
warnings will stick out like sore thumb anyway, and you won't need -Werror
to make them more annoying.

We have a long way until we are 100% warning free, but most of the warnings
come from upstream code. They have been fixed in later versions of
PostgreSQL, so they will go away as we merge with upstream.

Since commit a4d03bbc, "make dist" has
built both gzip- and bzip2-compressed tarballs.  However, this was
pretty useless, because our tarball build script didn't know about it
and proceeded to overwrite the bz2 file with new data.  Back-patch the
change to all active branches, so that creation of the tar.bz2 file
can be removed from the build script.

itself as libuuid, not libossp-uuid which was the only case expected by
our build support.  Install a configure test to determine which name
to use (and to check that the library is present at all).

databases with encodings that are incompatible with the server's LC_CTYPE
locale, when we can determine that (which we can on most modern platforms,
I believe).  C/POSIX locale is compatible with all encodings, of course,
so there is still some usefulness to CREATE DATABASE's ENCODING option,
but this will insulate us against all sorts of recurring complaints
caused by mismatched settings.

I moved initdb's existing LC_CTYPE-to-encoding mapping knowledge into
a new src/port/ file so it could be shared by CREATE DATABASE.

database.

installations whose pg_config program does not appear first in the PATH.
Per gripe from Eddie Stanley and subsequent discussions with Fabien Coelho
and others.

library.  New configure option --with-ossp-uuid to activate.

If this breaks things due to missing libxslt, then I'll have to
revert it, but let's see if it breaks the buildfarm.

Workarounds in case libxslt is missing include:
. don't configure with libxml, or
. don't build contrib modules from the contrib Makefile (use the individual module Makefiles instead), or
. change the xml2 Makefile

specify it explicitly in backend/Makefile.  Arrange for this value to
be known by get_stack_depth_rlimit() too.  Per suggestion from Magnus.

repeatedly.  Now that we don't have to worry about memory leaks from
glibc's qsort, we can safely put CHECK_FOR_INTERRUPTS into the tuplesort
comparators, as was requested a couple months ago.  Also, get rid of
non-reentrancy and an extra level of function call in tuplesort.c by
providing a variant qsort_arg() API that passes an extra void * argument
through to the comparison routine.  (We might want to use that in other
places too, I didn't look yet.)

an earlier discussion.  Centralize assumptions about what libpq depends
on in one place in Makefile.global.  I am unconvinced that this list
is complete, but since ecpg seems to have gotten along with just these
entries, we'll try it this way and see what happens.

than before.  Albe Laurenz (but editorialized heavily by me, so if it
doesn't work it's my fault).

Use initializer string length as size for character strings.
Added ecpg_config.h file that is created via configure.

by Robert Lor

-built-in mechanism through the -MP flag.  Adjust the file extensions to
look more like Automake practice.  This frees up the .d suffix for use by
DTrace.

no evidence that any currently-supported platform needs this, and good
reason to think that any platform that did need it couldn't use the static
libraries anyway --- libpq, at least, has circular references.  Removing
the code shuts up tsort warnings about the circular references on some
platforms.

--enable-depend it often tries to create the .deps directory twice and
bails out when it already exists due to a race condition of if doesn't
exist, then create.  This patch prevents mkdir from returning an error.

Kris Jurka

relocated after installation.  We can't trust the installation paths
inserted into Makefile.global by configure, so instead we must get the
paths from pg_config.  This requires extending pg_config to support all
the separately-configurable path names, but that was on TODO anyway.

of special case for Windows port.  Put a PG_TRY around most of createdb()
to ensure that we remove copied subdirectories on failure, even if the
failure happens while creating the pg_database row.  (I think this explains
Oliver Siegmar's recent report.)  Having done that, there's no need for
the fragile assumption that copydir() mustn't ereport(ERROR), so simplify
its API.  Eliminate the old code that used system("cp ...") to copy
subdirectories, in favor of using copydir() on all platforms.  This not
only should allow much better error reporting, but allows us to fsync
the created files before trusting that the copy has succeeded.

problems:

---------------------------------------------------------------------------

Support cross compilation by compiling "zic" with a native compiler.
This relies on the output of zic being platform independent, but that is
currently the case.

is used in the toplevel configure.  Per Marko Kreen.

relies on the output of zic being platform independent, but that is
currently the case.