[clang] [Clang] Fixes of builtin definitions after PR #68324. (PR #81022)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM, these fixes all look correct to me. The only thing that seemed somewhat off was with the `sync` functions taking a pointer to a `volatile` (that's not documented in GCC's docs, but I think the signature does make sense). Thank you for the fixes!

https://github.com/llvm/llvm-project/pull/81022