testsuite/97494 - adjust gcc.dg/vect/slp-11b.c

testsuite/97494 - adjust gcc.dg/vect/slp-11b.c

Support for loop SLP splitting exposed that slp-11b.c has
folding that breaks SLP discovery which isn't what was intended
when the testcase was written.  The following makes it SLP-able
and "only" run into the issue that a load permutation is required.

And tries to adjust the target selectors accordingly.

2021-01-18  Richard Biener  <rguenther@suse.de>

	PR testsuite/97494
	* gcc.dg/vect/slp-11b.c: Adjust.