middle-end/96814 - fix VECTOR_BOOLEAN_TYPE_P CTOR RTL expansion

middle-end/96814 - fix VECTOR_BOOLEAN_TYPE_P CTOR RTL expansion

The RTL expansion code for CTORs doesn't handle VECTOR_BOOLEAN_TYPE_P
with bit-precision elements correctly as the testcase shows before
the PR97085 fix.  The following makes it do the correct thing
(not 100% sure for CTOR of sub-vectors due to the lack of a testcase).

The alternative would be to assert such CTORs do not happen (and also
add IL verification for this).

The GIMPLE FE needs a way to declare the VECTOR_BOOLEAN_TYPE_P vectors
(thus the C FE needs that).

2020-09-25  Richard Biener  <rguenther@suse.de>

	PR middle-end/96814
	* expr.c (store_constructor): Handle VECTOR_BOOLEAN_TYPE_P
	CTORs correctly.

	* gcc.target/i386/pr96814.c: New testcase.