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

[Giulio Eulisse via llvm-commits]

ktf wrote:

Using @zygoloid suggestion it works on GCC (including 9.4, as tested on godbolt), macOS XCode 15, now waiting for the CI to verify Windows.

@kuhar my understanding of your PR seems to still trigger the -Wnon-template-friend warning on GCC.

Side note: does anyone know how to get LLVM work in godbolt? Using the vspkg package does not work for me (missing includes from llvm/.*).

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