[compiler-rt] Bfi precision (PR #66285)

[Matthias Braun via llvm-commits]

MatzeB wrote:

* Rebased on github/main
* Removed dependency on https://github.com/llvm/llvm-project/pull/67197 (updated more tests instead)
* Partly revived `test/Transforms/PGOProfile/bfi_verification.ll`: I can provoke some count mismatches by cranking up the numbers; though so far I cannot find a way to still provoke the situation where a block flips between hot/cold (as BFI chooses to loose precision on the low-end with this patch but hot/cold decisions happen at the high-end...)

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