[clang] Correctly compute conversion seq for args to fn with reversed param order (PR #68999)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

I think this is important that clang chooses not to error but only warn here as a clang extension (it already chooses to do so in cases when it the can match the function params([1](https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaOverload.cpp#L10274-L10290) and [2](https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaOverload.cpp#L14415-L14476))
Now that we correctly handle templated `operator==` in this PR, should we also relax the error here as well to a warning ? WDYT @zygoloid 

[GCC does the same](https://godbolt.org/z/Knrv66rd3).

https://github.com/llvm/llvm-project/pull/68999