tree-optimization/101264 - rework SLP "any" permute forward prop

tree-optimization/101264 - rework SLP "any" permute forward prop

This integrates the forward propagation of SLP "any" permutes into
the main propagation stage as a separate single-pass propagation
didn't work out.

2021-06-30  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101264
	* tree-vect-slp.c (vect_optimize_slp): Propagate the
	computed perm_in to all "any" permute successors
	we cannot de-duplicate immediately.

	* gfortran.dg/pr101264.f90: New testcase.