rs6000: Don't write "nor" as (not (ior () ())) (PR80618)

rs6000: Don't write "nor" as (not (ior () ())) (PR80618)

The canonical RTL for "nor" is (and (not ()) (not ())), and that is
indeed what we use in boolccv2df3_internal1.  So, the splitter for
*vector_uneq<mode> should use that form, not (not (ior () ())), which
does not match any pattern.

	PR target/80618
	* config/rs6000/rs6000.md (*vector_uneq<mode>): Write the nor in the
	splitter result in the canonical way.

From-SVN: r248763