[llvm] [InlineAsm] wrap ConstraintCode in enum class NFC (PR #66003)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave approved this pull request.

Thanks for making this refactoring, it looks reasonable to me. LGTM on 68k part.

https://github.com/llvm/llvm-project/pull/66003