[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 #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If the macro is not defined it's either a clang bug, or is intentional because
the implementation is not finished.

It is undefined for you to define any __cpp* macro yourself.