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

[Mehdi Amini via cfe-commits]

joker-eph wrote:

As an alternative: can this be just made a header-only implementation?
Since C++17 we can have `static inline` variables in a class (and `static constexpr` are by default inline: https://en.cppreference.com/w/cpp/language/inline.html



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