[llvm] Inline operator== and operator!= (PR #67958)

[Giulio Eulisse via llvm-commits]

ktf wrote:

Ping @kuhar @zygoloid @dwblaikie. This seems to work without warnings on all the compilers I managed to test (gcc 9.4.0 on godbolt, latest GCC on godbolt, macOS XCode 15, and of course the CI). Adapted from @zygoloid suggestion.

https://github.com/llvm/llvm-project/pull/67958