Should reject a requires-clause attached to a non-template function

[llvmbot]

Bugzilla Link	51831
Version	12.0
OS	Windows NT
Reporter	LLVM Bugzilla Contributor
CC	@zygoloid

Extended Description

Wrong code as follows is accepted by Clang:

#include <iostream>

template<> //#1
void foo(auto x) { std::cout << x; };

template<> //#2
void foo(int) requires(false) { std::cout << "int"; };

int main() { foo(1); }

In #​1, we have a template specialization, while no template function was defined before.
In #​2 we have requires-clause for not-template function.

Both #​1 and #​2 must be rejected.

[Quuxplusone]

The first part of this issue is a duplicate of #50294.
The second part can be reduced down to

void foo() requires true {}

Clang accepts, but it shouldn't.

[royjacobson]

Fixed by https://reviews.llvm.org/D125711

[llvmbot]

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