libstdc++: Disable over-zealous warnings about std::string copies [PR103332]
These warnings are triggered by perfectly valid code using std::string.
They're particularly bad when --enable-fully-dynamic-string is used,
because even std::string().begin() will give a warning.
Use pragmas to stop the troublesome warnings for copies done by
std::char_traits.
libstdc++-v3/ChangeLog:
PR libstdc++/103332
PR libstdc++/102958
PR libstdc++/103483
* include/bits/char_traits.h: Suppress stringop and array-bounds
warnings.