[BFI] Scale block frequencies with native 128-bit integers (NFC) (#239953)
Update setBlockFreqAndScale to use native 128 bit integers instead of
APInt if available, as this improves compile-time:
stage1-O3: -0.7%
stage1-ReleaseThinLTO: -0.08%
stage1-ReleaseLTO-g: -0.06%
stage1-aarch64-O3: -0.07%
stage2-O3: -0.07%
stage2-clang: -0.14%
https://llvm-compile-time-tracker.com/compare.php?from=f82380b4c3ff92a6293f03f7c02e40249ba10e13&to=b885f69205b43f51764127d753eaed4fd91a12e8&stat=instructions:u
Assisted-by: Opus 5.5
PR: https://github.com/llvm/llvm-project/pull/239953