tree-optimization/101207 - fix BB reduc permute elide with life stmts

This fixes breakage of live lane extracts from permuted loads we elide
from BB reduction vectorization by handling the un-permuting the same
as in the regular eliding code - apply the reverse permute to
both the scalar stmts and the load permutation.

2021-06-28  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101207
	* tree-vect-slp.c (vect_optimize_slp): Do BB reduction
	permute eliding for load permutations properly.

	* gcc.dg/vect/bb-slp-pr101207.c: New testcase.