[Bug libstdc++/54924] Warn for std::string constructor with wrong size

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54924

--- Comment #9 from Martin Sebor <msebor at gcc dot gnu.org> ---
Sadly, even with pr79214 fixed and pr79234 implemented, -Wno-system-headers
still somehow defeats the warning.