testsuite/105122 - adjust testcases after memcpy folding changes

testsuite/105122 - adjust testcases after memcpy folding changes

After r12-7931 we again honor MOVE_MAX when folding memcpy to
a load/store pair.  On i?86-*-* without SSE this now exposes the
change done in r12-2666-g29f0e955c97da0 which adjusts MOVE_MAX
from 16 to 4 on those targets.  This makes adjusting testcases
necessary that assume that we transform memcpy to load/store pairs
on GIMPLE for sizes larger or equal to 8.

2022-04-04  Richard Biener  <rguenther@suse.de>

	PR testsuite/105122
	* gcc.dg/memcpy-6.c: Adjust.
	* gcc.dg/strlenopt-73.c: Likewise.
	* gcc.dg/strlenopt-80.c: Likewise.