[4.0.0 Release] Release Candidate 1 source and binaries available

Source, binaries and docs for LLVM-4.0.0-rc2 are now available at
http://www.llvm.org/pre-releases/4.0.0/#rc2

Please try it out, run tests, build your favourite projects and file
bugs about anything that needs to be fixed, marking them as blockers
of http://llvm.org/pr31622.

Many things have been fixed since RC1, but there are still open issues
so we will need at least one more release candidate before the final
release.

Cheers,
Hans