[Bug libstdc++/124444] [16 Regression] debug _M_invalidate_if incompatible with C++20 since r16-5845

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124444

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
That would require adding pragmas to suppress:

...include/ext/concurrence.h:247: warning: call to non-'constexpr' function
'void __gnu_cxx::__mutex::lock()' [-Winvalid-constexpr]