[clang] [LLVM] Add new attribute `optdebug` to optimize for debugging (PR #66632)

[Arthur Eubanks via cfe-commits]

aeubanks wrote:

And same with `optsize`/`minsize` since those explicitly want as many simplifications as possible which conflicts with `optdebug`

https://github.com/llvm/llvm-project/pull/66632