[clang] Bfi precision (PR #66285)

[Matthias Braun via cfe-commits]

MatzeB wrote:

Seems this got introduced in https://reviews.llvm.org/D34312 with the rough idea that we shouldn't inline into parts of the code that `_builtin_expect(...)` deems unlikely. Which makes sense when you say it express it like this, but I guess numeric thresholds can go wrong...

https://github.com/llvm/llvm-project/pull/66285