HEADS UP: clang/llvm/lldb 3.7.0 imported

Hi all,

I upgraded clang, llvm, lldb, compiler-rt and libc++ to 3.7.0 release,
in head r288943.

Release notes for llvm and clang can be found here:
http://llvm.org/releases/3.7.0/docs/ReleaseNotes.html
http://llvm.org/releases/3.7.0/tools/clang/docs/ReleaseNotes.html

This was tested with several universe builds and a few ports exp-run
iterations, but if you run into something unexpected, please file a PR
and let me know. :-)

-Dimitry