Clang accepts constraints not satisfied void return type

[llvmbot]

Bugzilla Link	49844
Version	11.0
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@zygoloid

Extended Description

https://godbolt.org/z/YET98jcEW

template <class> concept C = false;

int main() {
  []() -> C auto {}();
}

clang accepts it.

[Quuxplusone]

This is now https://reviews.llvm.org/D119184

[llvmbot]

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