analyzer: round-trip pointer-equality through intptr_t

analyzer: round-trip pointer-equality through intptr_t

When investigating how the analyzer handles malloc/free of Cray pointers
in gfortran I noticed that that analyzer was losing information on
pointers that were cast to an integer type, and then back to a pointer
type again.

The root cause is that region_model::maybe_cast_1 was only preserving
the region_svalue-ness of the result if both types were pointers,
instead returning an unknown_svalue for a pointer-to-int cast.

This patch updates the above code so that it attempts to use a
region_svalue if *either* type is a pointer

Doing so allows the analyzer to recognize that the same underlying
region is in use through various casts through integer types.

gcc/analyzer/ChangeLog:
	* region-model.cc (region_model::maybe_cast_1): Attempt to provide
	a region_svalue if either type is a pointer, rather than if both
	types are pointers.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/torture/intptr_t.c: New test.