vect: Fix COND_EXPRs involving variant booleans [PR94727]

vect: Fix COND_EXPRs involving variant booleans [PR94727]

The previous patch for this PR handled separate comparisons.
However, as arm targets show, the same fix is needed when
handling comparisons embedded in a VEC_COND_EXPR.

Here too, the problem is that vect_get_constant_vectors will
calculate its own vector type, using truth_type_for on the
STMT_VINFO_VECTYPE, and the vectoriable_* routines need to be
consistent with that.

2020-04-28  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR tree-optimization/94727
	* tree-vect-stmts.c (vect_is_simple_cond): If both comparison
	operands are invariant booleans, use the mask type associated with the
	STMT_VINFO_VECTYPE.  Use !slp_node instead of !vectype to exclude SLP.
	(vectorizable_condition): Pass vectype unconditionally to
	vect_is_simple_cond.