[clang] [llvm] [clang][Inliner] Add opt-in inliner hints and implementation-file functions (PR #228074)

[Nikita Popov via cfe-commits]

nikic wrote:

Compile-time for enabling the flag: https://llvm-compile-time-tracker.com/compare.php?from=0d9fafe44cadd1d3344fc21bf5306c155de0cc6d&to=2218bf3001fc289e7760d9aa31cbc00c2e4fddfa&stat=instructions%3Au Large regressions on tramp3d-v4, but e.g. little impact on clang.

https://github.com/llvm/llvm-project/pull/228074