There is already a corresponding impl for `std::io::Write`. This change
will make the two traits more consistent.

- Headlines begin at 1st level now like the rest of the book
- All Headlines a blank line above and below
- Fix links in this chapter's TOC

r? @steveklabnik 

The style `[name][]` does not work with Pandoc, whereas `[name]` does. I hope hoedown accepts this as well.

r? @steveklabnik 

The style `[name][]` does not work with Pandoc, whereas `[name]` does.
I hope hoedown accepts this as well.

- Headlines begin at 1st level now like the rest of the book
- All Headlines a blank line above and below
- Fix links in this chapter's TOC

Redirect stdout on the python bogosity detector. This is printing
pwd to the terminal currently.

Reformat the bogus python/cmake messages so they format correctly.
echo does not always escape newlines (it doesn't here), and multiline
strings don't whitespace munch.

r? @alexcrichton 

Redirect stdout on the python bogosity detector. This is printing
pwd to the terminal currently.

Reformat the bogus python/cmake messages so they format correctly.
echo does not always escape newlines (it doesn't here), and multiline
strings don't whitespace munch.

This commit does some refactoring to make almost all of the `std::rt` private.
Specifically, the following items are no longer part of its API:

* DEFAULT_ERROR_CODE
* backtrace
* unwind
* args
* at_exit
* cleanup
* heap (this is just alloc::heap)
* min_stack
* util

The module is now tagged as `#[doc(hidden)]` as the only purpose it's serve is
an entry point for the `panic!` macro via the `begin_unwind` and
`begin_unwind_fmt` reexports.

This commit does some refactoring to make almost all of the `std::rt` private.
Specifically, the following items are no longer part of its API:

* DEFAULT_ERROR_CODE
* backtrace
* unwind
* args
* at_exit
* cleanup
* heap (this is just alloc::heap)
* min_stack
* util

The module is now tagged as `#[doc(hidden)]` as the only purpose it's serve is
an entry point for the `panic!` macro via the `begin_unwind` and
`begin_unwind_fmt` reexports.

Noticed these yesterday while reading libsyntax

When the inliner has to decided if it wants to inline a function A into an
internal function B, it first checks whether it would be more profitable
to inline B into its callees instead. This means that it has to analyze
B, which involves checking the assumption cache. Building the assumption
cache requires scanning the whole function, and because inlining
currently clears the assumption cache, this scan happens again and
again, getting even slower as the function grows from inlining.

As inlining the huge find functions isn't really useful anyway, we can
mark them as noinline, which skips the cost analysis and reduces compile
times by as much as 70%.

cc #28273

When the inliner has to decided if it wants to inline a function A into an
internal function B, it first checks whether it would be more profitable
to inline B into its callees instead. This means that it has to analyze
B, which involves checking the assumption cache. Building the assumption
cache requires scanning the whole function, and because inlining
currently clears the assumption cache, this scan happens again and
again, getting even slower as the function grows from inlining.

As inlining the huge find functions isn't really useful anyway, we can
mark them as noinline, which skips the cost analysis and reduces compile
times by as much as 70%.

cc #28273

llvm seems to be having some trouble optimizing the iterator-based string comparsion method into some equivalent to memcmp. This explicitly calls out to the memcmp intrinisic in order to allow llvm to generate better code. In some manual benchmarking, this memcmp-based approach is 20 times faster than the iterator approach.

r? @pnkfelix 

r? @Manishearth 

Closes #17994.

llvm seems to be having some trouble optimizing the iterator-based
string comparsion method into some equivalent to memcmp. This
explicitly calls out to the memcmp intrinisic in order to allow
llvm to generate better code. In some manual benchmarking, this
memcmp-based approach is 20 times faster than the iterator approach.

under OpenBSD, it could be have present multiples versions of gcc compiler:
  - gcc-4.2 (with patchs) : c/c++ compiler present in `/usr/bin`. It is unusable to build recent LLVM (so rustc too).
  - gcc/g++ -4.9 : c/c++ compiler, installed as third-party with "ports" mechanism. The compiler is installed in `/usr/local` as `egcc` (and `eg++`).

this PR adds probing for `egcc` for `CFG_GCC`, if the first probed `gcc` is too old. It will set `CC` and `CXX` too, in order to pass the variables to LLVM configure if builded.

please note this PR is a first step in order to build rustc under OpenBSD with unpatched tree.

r? @alexcrichton

cc @brson @dhuseby 

Fixes #27616.

r? @pnkfelix 

Closes #17994.

This was @steveklabnik's idea. Thanks @BurntSushi for the awesome blog post!
r? @steveklabnik 

Fix the following error when running configure with llvm 3.8svn:

configure: error: bad LLVM version: 3.8.0svn, need >=3.5

depending of the compiler used, jemalloc configure don't detect
correctly some parameters.

Closes #22638.
Closes #22872.
Closes #23024.
Closes #23046.

Closes #22638.
Closes #22872.
Closes #23024.
Closes #23046.

if default CFG_GCC is too old, probe also egcc (which is gcc from
ports).

set CC/CXX too, in order to pass them to LLVM

r? @steveklabnik

NFC.