[clang] [Clang] Make enums trivially equality comparable (PR #133587)

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halbi2 wrote:

@philnik777 Is anything else blocking this patch to fix #132672? Could you just change the commit message to what @shafik suggested and merge it please?

> [clang] Make enums trivially equality comparable
>
> std::equal(std::byte) currently has sub-optimal codegen due to enum types not being recognized as trivially comparable. In order to fix this we make them trivially comparable. In the process I factored out into a standalone function EqualityComparisonIsDefaulted.

https://github.com/llvm/llvm-project/pull/133587