Prune "return" after llvm_unreachable(). It was redundant.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190774 91177308-0d34-0410-b5e6-96231b3b80d8
Make F16C feature imply AVX. Matches GCC behavior.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190776 91177308-0d34-0410-b5e6-96231b3b80d8