[3.8 Release] Release Candidate 1 source and binaries available

Hello everyone,

Source and binaries for LLVM-3.8.0-rc1 are now available at

(Binaries for some platforms are still missing, but I figured it was
time to get this out there.)

Please try it, run tests, build your favourite projects, and *file
bugs* about anything that doesn't work and needs to be fixed for the
release. Please CC me on any findings.