middle-end/97521 - always use single-bit bools in mask vector types

middle-end/97521 - always use single-bit bools in mask vector types

This makes us always use a single-bit boolean type component type
for integer mode mask VECTOR_BOOLEAN_TYPE_P to match the RTL and target
representation.  This aovids the need for magic translation and
the inconsistencies from the translation requirement now that
we expose temporaries of those types on the GIMPLE level.

2020-10-23  Richard Biener  <rguenther@suse.de>

	PR middle-end/97521
	* expr.c (const_scalar_mask_from_tree): Remove.
	(expand_expr_real_1): Always VIEW_CONVERT integer mode
	vector constants to an integer type.
	* tree.c (build_truth_vector_type_for_mode): Use a single-bit
	boolean component type for non-vector-mode mask_mode.

	* gcc.target/i386/pr97521.c: New testcase.