sparc: refactor sparc64 isnan{f} selector to C

sparc: refactor sparc64 isnan{f} selector to C

This patch refactors the sparc64 ifunc selector to a C implementation.
Also, the generic symbol is moved to its own implementation file
(s_isnan{f}-generic.S).

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

	* sysdeps/sparc/sparc64/fpu/multiarch/Makefile (sysdeps_calls):
	Add s_isnanf-generic and s_isnan-generic objects.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_isnan-generic.S: New file.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_isnanf-generic.S: Likewise.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_isnan.c: Likewise.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_isnanf.c: Likewise.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_isnan.S: Remove file.
	* sysdeps/sparc/sparc64/fpu/multiarch/s_isnanf.S: Likewise.

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