libstdc++: Fix symbol versioning for Solaris 11.3 [PR103407]

libstdc++: Fix symbol versioning for Solaris 11.3 [PR103407]

The new std::from_chars implementation means that those symbols are now
defined on Solaris 11.3, which lacks uselocale. They were not present in
gcc-11, but the linker script gives them the GLIBCXX_3.4.29 symbol
version because that is the version where they appeared for systems with
uselocale.

This makes the version for those symbols depend on whether uselocale is
available or not, so that they get version GLIBCXX_3.4.30 on targets
where they weren't defined in gcc-11.

In order to avoid needing separate ABI baseline files for Solaris 11.3
and 11.4, the ABI checker program now treats the floating-point
std::from_chars overloads as undesignated if they are not found in the
baseline symbols file. This means they can be left out of the SOlaris
baseline without causing the check-abi target to fail.

libstdc++-v3/ChangeLog:

	PR libstdc++/103407
	* config/abi/pre/gnu.ver: Make version for std::from_chars
	depend on HAVE_USELOCALE macro.
	* testsuite/util/testsuite_abi.cc (compare_symbols): Treat
	std::from_chars for floating-point types as undesignated if
	not found in the baseline symbols file.