[Bug libstdc++/109299] [12/13 Regression] wrong warning on std::wstring with -O2 -std=c++20 -D_FORTIFY_SOURCE=2

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109299

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And the reason I put the hint in _M_is_local() not in the function giving the
warning is that it might help in other functions too.

I haven't tested it yet though.