[clang] [Clang] Add __builtin_bswapg (PR #162433)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> I accidentally added a large number of unintended reviewers. Could you help me remove them?

I believe I've got it back to the right set :D

How did you update your branch? (My suspicion is that something about that caused GitHub to suggest every person involved in all the merged PRs)

https://github.com/llvm/llvm-project/pull/162433