Use libm_alias_ldouble for SPARC fabsl.

This patch makes SPARC fabsl implementation use libm_alias_ldouble, to
prepare them for also defining _Float128 function aliases.

Tested with build-many-glibcs.py that installed stripped shared
libraries (sparc64-linux-gnu and sparcv9-linux-gnu) are unchanged by
the patch.

	* sysdeps/sparc/sparc32/fpu/s_fabsl.c: Include
	<libm-alias-ldouble.h>.
	(fabsl): Define using libm_alias_ldouble.
	* sysdeps/sparc/sparc64/fpu/s_fabsl.c: Include
	<libm-alias-ldouble.h>.
	(fabsl): Define using libm_alias_ldouble.