[clang] [llvm] Singleton hack of fixing static initialisation order fiasco (PR #154541)

[Mircea Trofin via cfe-commits]

https://github.com/mtrofin approved this pull request.

lgtm, just please remove the unrelated fix in MLInlineAdvisor (the follow-up PR, if you want to do it, doesn't need anything stuffy - just label the title as "[NFC]" - because it's not changing any behavior - and just say something as simple as "made a member static in MLInlineAdvisor" or something like that.

https://github.com/llvm/llvm-project/pull/154541