PR analyzer/93546 reports an ICE within region_model::add_region_for_type
when merging two region_models each containing a label pointer.  The
two labels are stored as pointers to symbolic_regions, but these regions
were created with NULL type, leading to an assertion failure when a
merged copy is created.

The labels themselves have void (but not NULL) type.

This patch updates make_region_for_type to use the type of the decl when
creating such regions, rather than implicitly setting the region's type
to NULL, fixing the ICE.

gcc/analyzer/ChangeLog:
	PR analyzer/93546
	* region-model.cc (region_model::on_call_pre): Update for new
	param of symbolic_region ctor.
	(region_model::deref_rvalue): Likewise.
	(region_model::add_new_malloc_region): Likewise.
	(make_region_for_type): Likewise, preserving type.
	* region-model.h (symbolic_region::symbolic_region): Add "type"
	param and pass it to base class ctor.

gcc/testsuite/ChangeLog:
	PR analyzer/93546
	* gcc.dg/analyzer/pr93546.c: New test.