So far, MingW shared libraries were named like this

  libeay32.dll + libeay32.dll.a
  ssleay32.dll + ssleay32.dll.a

That naming scheme is antiquated, a reminicense of SSLeay.  We're
therefore changing the scheme to something that's more like the rest
of OpenSSL.

There are two factors to remember:

  - Windows libraries have no recorded SOvers, which means that the
    shared library version must be encoded in the name.  According to
    some, it's unwise to encode extra periods in a Windows file name,
    so we convert version number periods to underscores.
  - MingW has multilib ability.  However, DLLs need to reside with the
    binaries that use them, so to allow both 32-bit and 64-bit DLLs to
    reside in the same place, we add '-x64' in the name of the 64-bit
    ones.

The resulting name scheme (for SOver 1.1) is this:

  on x86:
  libcrypto-1_1.dll + libcrypto.dll.a
  libssl-1_1.dll + libssl.dll.a

  on x86_64:
  libcrypto-1_1-x64.dll + libcrypto.dll.a
  libssl-1_1-x64.dll + libssl.dll.a

An observation is that the import lib is the same for both
architectures.  Not to worry, though, as they will be installed in
PREFIX/lib/ for x86 and PREFIX/lib64/ for x86_64.

As a side effect, MingW got its own targets in Makefile.shared.
link_dso.mingw-shared and link_app.mingw-shared are aliases for the
corresponding cygwin-shared targets.  link_shlib.mingw-shared is,
however, a target separated from the cygwin one.
Reviewed-by: NAndy Polyakov <appro@openssl.org>

As part of this, change util/mkdef.pl to stop adding libraries to
depend on in its output.  mkdef.pl should ONLY output a symbol
vector.

Because symbol names can't be longer than 31 characters, we use the
compiler to shorten those that are longer down to 23 characters plus
an 8 character CRC.  To make sure users of our header files will pick
up on that automatically, add the DEC C supported extra headers files
__decc_include_prologue.h and __decc_include_epilogue.h.

Furthermore, we add a config.com, so VMS people can configure just as
comfortably as any Unix folks, thusly:

    @config
Reviewed-by: NRich Salz <rsalz@openssl.org>

Cygwin and Mingw name their libraries a bit differently from the rest
of the POSIXly universe, we need to adapt to that.

In Makefile.tmpl, it means that some hunks will only be output
conditionally.

This also means that shared_extension for the Cygwin and Mingw
configurations in Configurations/10-main.conf are changing from .dll.a
to .dll.  Makefile.shared does a fine job without having them
specified, and it's much easier to work with tucking an extra .a at
the end of files in the installation recipes than any amount of name
rewrites, especially with the support of the SHARED_NAME in the top
build.info.
Reviewed-by: NRich Salz <rsalz@openssl.org>

In build.info files, make the include directory in the build directory
absolute, or Configure will think it should be added to the source
directory top.  Configure will turn it into a relative path if
possible.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Now that we have the foundation for the "unified" build scheme in
place, we add build.info files.  They have been generated from the
Makefiles in the same directories.  Things that are platform specific
will appear in later commits.
Reviewed-by: NAndy Polyakov <appro@openssl.org>