[llvm] Allow PTO to be modified in PassBuilder (PR #92821)

[Arthur Eubanks via llvm-commits]

https://github.com/aeubanks commented:

this seems like something that should be constant after creating the PassBuilder. what's wrong with creating a completely new PassBuilder if you want a different PTO? do you actually use this functionality?

https://github.com/llvm/llvm-project/pull/92821