[clang] [clang] Implement __builtin_stdc_rotate_left, __builtin_stdc_rotate_right (PR #160259)

[Nikolas Klauser via cfe-commits]

https://github.com/philnik777 approved this pull request.

LGTM, but let's wait for one of the Clang people to take another look.

https://github.com/llvm/llvm-project/pull/160259