[clang] [llvm] [GlobalOpt] Add TTI interface useFastCCForInternalCall for FASTCC (PR #164768)

[Alex Bezzubikov via llvm-commits]

zuban32 wrote:

A function could be external before LTO stage, and become internal only after LTO symbol resolution. I.e. we're linking against some older object file which has the function compiled with some older definition of the target feature, and the calls to that function in a new module would still become fastcc.

https://github.com/llvm/llvm-project/pull/164768