tree-optimization/104152 - add missing check for SLP constant build

This adds a missing check to verify we can actually build an
invariant vector from components when SLP vectorizing an associatable
chain.

2022-01-21  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/104152
	* tree-vect-slp.cc (vect_build_slp_tree_2): Add missing
	can_duplicate_and_interleave_p check.

	* gcc.dg/vect/pr104152.c: New testcase.
2 files changed