Fix sparc64 build with GCC 9.

Similar to the x86_64 and armv7 build issues, glibc fails to build for
sparc64 with current mainline GCC because of aliases declared in the
course of defining IFUNCs, which copy their attributes from a header
declaration, ending up with fewer attributes than the (built-in)
string function they alias.  This patch fixes the issue similarly to
the fixes for those other architectures.

Tested with build-many-glibcs.py compilers build for
sparc64-linux-gnu.

	* sysdeps/sparc/sparc-ifunc.h [SHARED]
	(sparc_ifunc_redirected_hidden_def): Use __attribute_copy__ to
	copy attributes from name.