tree-optimization/99510 - fix type reuse of build_aligned_type

tree-optimization/99510 - fix type reuse of build_aligned_type

The fix for PR94775 added more strict checking for type reuse
to check_aligned_type, specifically matching TYPE_USER_ALIGN.
But then build_aligned_type sets TYPE_USER_ALIGN on the built
variant so if the type we build an aligned variant for does not
have TYPE_USER_ALIGN we'll never re-use the newly created aligned
variant.  This results in ~35000 identical variants being created
for polyhedron doduc.

The following instead checks that the candidate has TYPE_USER_ALIGN set.

2021-03-10  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/99510
	* tree.c (check_aligned_type): Check that the candidate
	has TYPE_USER_ALIGN set instead of matching with the
	original type.