[clang] [Clang] Emit LLVM flatten attribute instead of per-callsite alwaysinline (PR #188615)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Perhaps @efriedma-quic should take a look as codegen maintainer?

https://github.com/llvm/llvm-project/pull/188615