Implementing friend operator with two exclusive requires clauses but same name of requirement causes "error: redefinition of 'operator<<'"

[gsamatt]

This does not compile with clang 18 but it does with clang 17:
https://godbolt.org/z/orMfTfxMd

This would compile with both compiler as it uses a different name for the requirement:
https://godbolt.org/z/Mjxq54abb

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (gsamatt)

This does not compile with clang 18 but it does with clang 17: https://godbolt.org/z/orMfTfxMd

This would compile with both compiler as it uses a different name for the requirement:
https://godbolt.org/z/Mjxq54abb

[Sirraide]

Reduced (https://godbolt.org/z/Yzcdca6a1):

struct A {
    template <typename M> static constexpr bool C = true;
    template <typename M> friend void f() requires (C<M>) {}
};

struct B {
    template <typename M> static constexpr bool C = false;
    template <typename M> friend void f() requires (C<M>) {}
};

[zyn0217]

This seemed to have been fixed at some point within clang 21:

https://godbolt.org/z/MTfEeo1fG
https://godbolt.org/z/Kjjqf7jbh