[Bug libstdc++/92850] clang has already supported concepts in latest trunk. However it does not define __cpp_concepts macro. I defined it but crashes clang compiler

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92850

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to fdlbxtqi from comment #2)
> "Are you sure concepts are fully implemented in clang?"
> 
> Yes, but feature testing macro is missing.

No, it very obviously doesn't support concepts:

https://godbolt.org/z/n4AkpC

So that will be why it doesn't define the macro.