sparc: refactor sparc32 copysign selector to C

This patch refactors the sparc32 ifunc selector to a C implementation.
Also, the generic symbol is moved to its own implementation file
s_copysign{f}-generic.S).

Checked on sparc64-linux-gnu and sparcv9-linux-gnu.

	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/Makefile
	(sysdep_calls): New rule.
	(sysdep_routines): Use sysdep_calls as base.
	(libm-sysdep_routines): Add generic rule for symbols shared with
	libc.  Add s_copysign-generic and s_copysign-generic objects.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_copysign-generic.S:
	New file.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_copysign.c: Likewise.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_copysignf-generic.S:
	Likewise.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_copysignf.c: Likewise.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_copysign.S: Remove file.
	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_copysignf.S: Likewise.

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>