[llvm] Avoid BlockFrequency overflow problems (PR #66280)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata commented:

LGTM.  Thank you for updating the patch!  (And even bigger thank you for paying attention to the block frequencies in the first place!)

Please be sure to update the commit message also as we no longer use `__attribute__((warn_unused_result))`.

https://github.com/llvm/llvm-project/pull/66280