Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
5.0.0 release (upstream r312559).

Release notes for llvm, clang and lld will be available here soon:
http://releases.llvm.org/5.0.0/docs/ReleaseNotes.html
http://releases.llvm.org/5.0.0/tools/clang/docs/ReleaseNotes.html
http://releases.llvm.org/5.0.0/tools/lld/docs/ReleaseNotes.html

Relnotes: yes
MFC after: 1 month
X-MFC-with: r321369