[llvm] [PGO] Drive profile validator from opt (PR #147418)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM.

Documentation in `llvm/docs/CMake.rst` might still be nice, but this is sort of a very specific debug option that might not fit in super well there, so whatever you want to do works.

https://github.com/llvm/llvm-project/pull/147418