Upgrade LLVM

This comes with a number of fixes to be compatible with upstream LLVM:

* Previously all monomorphizations of "mem::size_of()" would receive the same
  symbol. In the past LLVM would silently rename duplicated symbols, but it
  appears to now be dropping the duplicate symbols and functions now. The symbol
  names of monomorphized functions are now no longer solely based on the type of
  the function, but rather the type and the unique hash for the
  monomorphization.

* Split stacks are no longer a global feature controlled by a flag in LLVM.
  Instead, they are opt-in on a per-function basis through a function attribute.
  The rust #[no_split_stack] attribute will disable this, otherwise all
  functions have #[split_stack] attached to them.

* The compare and swap instruction now takes two atomic orderings, one for the
  successful case and one for the failure case. LLVM internally has an
  implementation of calculating the appropriate failure ordering given a
  particular success ordering (previously only a success ordering was
  specified), and I copied that into the intrinsic translation so the failure
  ordering isn't supplied on a source level for now.

* Minor tweaks to LLVM's API in terms of debuginfo, naming, c++11 conventions,
  etc.
configure: Enable libc++ with LLVM with clang

When clang is enabled, also pass through --enable-libcpp to LLVM's configure
command line to help it pick up the most recent c++ runtime library. This also
changes the mklldeps.py script to pick up on whether LLVM was linked against
stdc++ or c++ based on the --cxxflags that llvm-config prints.

In an ongoing attempt to update LLVM, the bots need to update their C compilers
to something that supports c++11 (LLVM recently switched). The OSX bots are
running Lion (10.7), which only supports up to gcc 4.2 and clang 3.2. Apparently
the libstdc++ is too old (even on the most updated command line tools) for LLVM,
but using libc++ instead appears to work just fine.
configure: Enable clang for older OSX gcc versions

OSX often has a more recent version of clang than it does for GCC. When an older
version of gcc is detected on OSX, the --enable-clang flag is implicitly
enabled.
etc: The --system-libs flag is LLVM 3.5+

Older version of LLVM did not have this flag, so we need to fall back to our
previous library detection when using older versions of LLVM.
llvm: Add an option to statically link libstdc++

The goal of the snapshot bots is to produce binaries which can run in as many
locations as possible. Currently we build on Centos 6 for this reason, but with
LLVM's update to C++11, this reduces the number of platforms that we could
possibly run on.

This adds a --enable-llvm-static-stdcpp option to the ./configure script for
Rust which will enable building a librustc with a static dependence on
libstdc++. This normally isn't necessary, but this option can be used on the
snapshot builders in order to continue to make binaries which should be able to
run in as many locations as possible.
rustc: Hint to the linker about static/shared libs

If a linker finds both a static and a dynamic version of the same library, then
the linker often chooses the dynamic version. This is surprising when a native
library is specified as being "static" in rust source. This modifies the linker
command line to obey the hints given in rust source files and instructing the
linker to prefer a particular version of a found library.

Unfortunately, this patch has no effect on osx because the linker supports
no such hint, and it also has no effect on windows because the linker apparently
just ignores it. For now this is predominately used to enable the previous patch
of linking to libstdc++ statically, but more support would need to be added for
this in the future if we wanted to officially support it.

cc #12557 (doesn't close because it doesn't support OSX and windows)
Remove rule that is confusing

The original text stated that one should only return a unique or managed pointer if you were given one in the first place. This makes it sound as if the function *should* return a unique pointer if it were given a unique pointer. The rest of the section goes on to describe why this is bad, and the example of bad code does exactly what the rule just said to do.

I reworded the original rule into a reference to the more concise rule mentioned at the bottom of the section, which helps add emphasis (a la 'it bears repeating').
auto merge of #13585 : brandonw/rust/patch-1, r=cmr

The original text stated that one should only return a unique or managed pointer if you were given one in the first place. This makes it sound as if the function *should* return a unique pointer if it were given a unique pointer. The rest of the section goes on to describe why this is bad, and the example of bad code does exactly what the rule just said to do.

I reworded the original rule into a reference to the more concise rule mentioned at the bottom of the section, which helps add emphasis (a la 'it bears repeating').
std: Make ~[T] no longer a growable vector

This removes all resizability support for ~[T] vectors in preparation of DST.
The only growable vector remaining is Vec<T>. In summary, the following methods
from ~[T] and various functions were removed. Each method/function has an
equivalent on the Vec type in std::vec unless otherwise stated.

* slice::OwnedCloneableVector
* slice::OwnedEqVector
* slice::append
* slice::append_one
* slice::build (no replacement)
* slice::bytes::push_bytes
* slice::from_elem
* slice::from_fn
* slice::with_capacity
* ~[T].capacity()
* ~[T].clear()
* ~[T].dedup()
* ~[T].extend()
* ~[T].grow()
* ~[T].grow_fn()
* ~[T].grow_set()
* ~[T].insert()
* ~[T].pop()
* ~[T].push()
* ~[T].push_all()
* ~[T].push_all_move()
* ~[T].remove()
* ~[T].reserve()
* ~[T].reserve_additional()
* ~[T].reserve_exect()
* ~[T].retain()
* ~[T].set_len()
* ~[T].shift()
* ~[T].shrink_to_fit()
* ~[T].swap_remove()
* ~[T].truncate()
* ~[T].unshift()
* ~str.clear()
* ~str.set_len()
* ~str.truncate()

Note that no other API changes were made. Existing apis that took or returned
~[T] continue to do so.

[breaking-change]
std: Fail more gracefully on thread spawn errors

On windows, correctly check for errors when spawning threads, and on both
windows and unix handle the error more gracefully rather than printing an opaque
assertion failure.

Closes #13589
Update the rest of the compiler with ~[T] changes
Add another case where cindent is correct

When calling a function, or anything with nested parens,
default to cindent's indent. The least error-prone way I
could think of identifying this is to look for a line
that ends with a ',', as well as a non-zero number of
any character except parens before the comma, and
then an open paren.

This will overlap with the previous rule accounting for
function definitions, but that should be fine because
it is also using cindent.
auto merge of #13588 : alexcrichton/rust/no-more-growing, r=thestinger

This is all in preparation for DST. This removes all the growable/shrinkable methods from `~[T]`.
Add git to README.md dependency list because configure requires it
auto merge of #13601 : mdinger/rust/readme, r=brson

Configure required git be installed so this should be added to the dependencies list.  If it's only required when using git, a note could also be added.
auto merge of #13600 : brandonw/rust/master, r=brson

When calling a function, or anything with nested parens,
default to cindent's indent. The least error-prone way I
could think of identifying this is to look for a line
that ends with a ',', as well as a non-zero number of
any character except parens before the comma, and
then an open paren.

This will overlap with the previous rule accounting for
function definitions, but that should be fine because
it is also using cindent.
Fix smallest-hello-world.rs interaction with `puts`

It now hands `puts` a zero-terminated string, like it expects.

Fix #13603.
Fix a couple places in docs where try_send wasn't changed to send_opt
debuginfo: Clamp the maximum dwarf version to 3

This is a consequence of #13611 and our bots running a "fairly old" gdb which
doesn't understand the newer versions of dwarf.
vim: Add StrBuf as type to hilighting