[compiler-rt] [profile] Fix bounds checks in profile merging (PR #118782)

[NAKAMURA Takumi via llvm-commits]

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

Looks good. Please wait for another opinion.

For bound-free arithmetic, shall we cast to uintptr_t, ultimately?

https://github.com/llvm/llvm-project/pull/118782