llvm: bump LLVM/Clang to pre-3.6

Clang after 3.5 added support for capturing non-POD VLAs in lambdas.
Also resolves some Clang asserts in CMSSW.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
py2-dxr: update to compile with Clang 3.6

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #1220 from davidlt/bump-llvm-clang-pre-36

Update LLVM/Clang to pre-3.6