HEADS-UP: Merged llvm/clang 5.0.0 into -CURRENT (as of r321369)

Hi,

I have merged clang, llvm, lld, lldb, compiler-rt and libc++ 5.0.0
(trunk r308421) into head.  Universe builds went just fine, but if you
encounter any snags during world and/or kernel builds, please file PRs.

Since upstream has just created their 5.0.0 release branch, this is a
good month to shake out any remaining issues for FreeBSD.  If you are
certain bugs or regressions you encounter are due to upstream, file PRs
there, but otherwise, just report them on the FreeBSD bug tracker.

-Dimitry