[clang] [Clang][NFC] Code cleanup in CGBuiltin.cpp (PR #132060)

[Aaron Ballman via cfe-commits]

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

Changes LGTM though I've added @efriedma-quic as a codegen code owner just in case he's got different opinions.

https://github.com/llvm/llvm-project/pull/132060