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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

At some point we should split Support into "ReallySupport" and "RandomStuffThatIRAndCodeGenUse"

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