Update llvm to trunk r256633.

Merge llvm trunk r238337 from ^/vendor/llvm/dist, resolve conflicts, and
preserve our customizations, where necessary.

Merge llvm 3.5.0 release from ^/vendor/llvm/dist, resolve conflicts, and
preserve our customizations, where necessary.

Upgrade our copy of llvm/clang to 3.4 release. This version supports
all of the features in the current working draft of the upcoming C++
standard, provisionally named C++1y.

The code generator's p

Upgrade our copy of llvm/clang to 3.4 release. This version supports
all of the features in the current working draft of the upcoming C++
standard, provisionally named C++1y.

The code generator's performance is greatly increased, and the loop
auto-vectorizer is now enabled at -Os and -O2 in addition to -O3. The
PowerPC backend has made several major improvements to code generation
quality and compile time, and the X86, SPARC, ARM32, Aarch64 and SystemZ
backends have all seen major feature work.

Release notes for llvm and clang can be found here:
<http://llvm.org/releases/3.4/docs/ReleaseNotes.html>
<http://llvm.org/releases/3.4/tools/clang/docs/ReleaseNotes.html>

MFC after: 1 month

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Upgrade our copy of llvm/clang to 3.3 release.

Release notes are still in the works, these will follow soon.

MFC after: 1 month