[compiler-rt] [llvm] [mlir] [clang-tools-extra] [clang] [clang] Fix a bug with qualified name lookup into current instantiation (PR #73018)

[via cfe-commits]

john-brawn-arm wrote:

As a result of this commit clang no longer gives an error for
```
template <int A> struct X {
  enum E { a };
};

template <int A> struct Y : X<A> {
  Y::E m;
};
```
where gcc (though not msvc) gives an error: https://godbolt.org/z/qGfnzhfsK

https://github.com/llvm/llvm-project/pull/73018