Fix build on pre-v9 32-bit Sparc.

We cannot use fnegd in this code, as fnegd was added in v9.
Only fnegs exists in v8 and earlier.

	[BZ #15985]
	* sysdeps/sparc/sparc32/fpu/s_fdim.S (__fdim): Do not use fnegd
	on pre-v9 cpus, use a fnegs+fmovs sequence instead.