[clang] [llvm] [Clang][LFI] Add mlfi Clang option to control LFI subtarget features (PR #204689)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Was there an RFC for this? (Mostly looking for background info; does GCC support this under this spelling, is an `-m` flag the right design, etc?)

https://github.com/llvm/llvm-project/pull/204689