[clang] [flang] [llvm] [mlir] [Support][NFC] Move OptimizationLevel to the Support directory (PR #157057)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Perhaps the TargetParser directory is more suitable for them. Not sure what they are used for.

It's closer but not quite right. I think there probably should be some kind of ABI-information for this sort of stuff. TargetParser is more specific to frontend-backend interactions 

https://github.com/llvm/llvm-project/pull/157057