libstdc++: Disable over-zealous warnings about std::string copies [PR103332]

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.