[llvm] [llvm][Support] Enable pass timing in StandardInstrumentations constr… (PR #108983)

[Tarun Prabhu via llvm-commits]

tarunprabhu wrote:

I think it would be acceptable, for `flang` at least, to only enable timing of the middle-end passes for now. But I would need to solicit more feedback from that community to be certain. It would be better if we didn't have to resort to setting global variables there. Such concerns [have also been raised there](https://github.com/llvm/llvm-project/pull/106141#issuecomment-2313352498) for some other cases too.

My intention was to try and set things up so we could slowly migrate to using constructor arguments to enable timings in the pass manager instead of relying solely on globals.

https://github.com/llvm/llvm-project/pull/108983