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

[Sergei Barannikov via cfe-commits]

s-barannikov wrote:

> > I always thought of ADT and Support libraries as being useful for other projects
> 
> That would be nice, and I'd love to move libSupport at the top-level (only the pieces that matches the "generic aspect" of it), but the reality today is that beyond filesystem abstractions, thread pool, and other generic things, there are also things like `X86DisassemblerDecoderCommon.h`, `MSP430Attributes.h`, `AMDHSAKernelDescriptor.h`, `AArch64AttributeParser.h`, `RISCVISAUtils.h`, etc.

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

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