Expose __builtin_bswap16.

GCC has always supported this on PowerPC and 4.8 supports it on all platforms,
so it's a good idea to expose it in clang too. LLVM supports this on all targets.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165362 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed