[clang] [clang][FMV] Direct-call FMV callees from FMV callers (PR #80093)

[Jon Roelofs via cfe-commits]

jroelofs wrote:

Fair. I'll give that a shot.

Doing it in opt has another big advantage I only just realized: it allows LTO to do the transformation.

https://github.com/llvm/llvm-project/pull/80093