[clang] [Clang][Sema] Fix missing warning when comparing mismatched enums in … (PR #81418)

[Erich Keane via cfe-commits]

erichkeane wrote:

> For what it's worth, this change adds several instances of `-Wenum-enum-conversion` for the Linux kernel: [ClangBuiltLinux/linux#2002](https://github.com/ClangBuiltLinux/linux/issues/2002). I assume this is intentional given the nature of the change as a whole but neither the tests nor the release notes seem to really reflect that. In case it is a bug that this change affected that, consider this a report :)

You're correct, those are intentional.  `https://github.com/llvm/llvm-project/pull/81418/files#diff-f240d794093a226da48919a27929148597edd1460a1d38b0decbced3fc153ddc`  specifically covers 'conversions' but arithmetic operations are also covered by that warning. 

https://github.com/llvm/llvm-project/pull/81418