[llvm] [ubsan][hwasan] Let mixing filters (PR #100680)

[Thurston Dang via llvm-commits]

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

Is `ShouldRemoveRandom() || ShouldRemoveHot(BB);` the most interpretable way to combine these filters? e.g., suppose ClRandomSkipRate = 0.6 and ClHotPercentileCutoff is 750000 (75%th). What is the percentage of checks that is skipped?

Perhaps another approach could be to have three settings:
- hot percentile cutoff: this by default doesn't skip anything
- random skip percentage for hot functions
- random skip percentage for cold functions
The fully random case is equivalent to setting the same random skip percentage for hot and cold functions. The skip-hot-functions-only case is equivalent to setting the random skip percentage for cold functions to zero.

https://github.com/llvm/llvm-project/pull/100680