[clang] [CIR] Added case for builtins in CIRGen (PR #218852)

[Kunal Dubey via cfe-commits]

xakep8 wrote:

Hey @andykaylor I've addressed the reviews and I've also handled the lowering of stdc_memreverse8, I mirrored the classic CodeGen behaviour here.

https://github.com/llvm/llvm-project/pull/218852