Clang C++20 Feature: P1972R0 - US105 Check satisfaction of constraints for non-templates when forming pointer to function

[tstellar]

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id: P1972R0
paper: https://wg21.link/p1972r0

[llvmbot]

@llvm/issue-subscribers-c-20

[royjacobson]

Can we close this issue? @erichkeane

AFAICT we've been checking for constraints there ever since clang 10: https://godbolt.org/z/9PEYescnW

[erichkeane]

Yep. We can close this, but I need to update https://clang.llvm.org/cxx_status.html FIRST. I'll do both.

[erichkeane]

Done here: 281b7ee