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

[Richard Smith via cfe-commits]

zygoloid wrote:

> I'm not sure I understand why gcc is giving an error in https://godbolt.org/z/qGfnzhfsK. It doesn't give an error with `typename` keyword and I think there shouldn't be any difference since `Y::E` refers to current instantiation and is being used by class member declaration so no `typename` required. cc @shafik @cor3ntin @zygoloid for an opinion.

This looks like a GCC bug to me. I think the presence or absence of `typename` isn't supposed to make a difference in an implicit typename context.

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