Upgrade our copies of clang, llvm, lldb and compiler-rt to 3.8.0
release.

Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
support to build; see UPDATING for more information.

Release notes for llvm and clang will soon be available here:
http://llvm.org/releases/3.8.0/docs/ReleaseNotes.html
http://llvm.org/releases/3.8.0/tools/clang/docs/ReleaseNotes.html

Thanks to Ed Maste, Roman Divacky, Davide Italiano and Antoine Brodin
for their help.

Relnotes: yes