analyzer: casting all zeroes should give all zeroes [PR113333]

analyzer: casting all zeroes should give all zeroes [PR113333]

In particular, accessing the result of *calloc (1, SZ) (if non-NULL)
should be known to be all zeroes.

gcc/analyzer/ChangeLog:
	PR analyzer/113333
	* region-model-manager.cc
	(region_model_manager::maybe_fold_unaryop): Casting all zeroes
	should give all zeroes.

gcc/testsuite/ChangeLog:
	PR analyzer/113333
	* c-c++-common/analyzer/calloc-1.c: Add tests.
	* c-c++-common/analyzer/pr96639.c: Update expected results.
	* gcc.dg/analyzer/data-model-9.c: Likewise.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>