Some Mock constructors insert the pointer to the Mock itself into a
global registry. Since GCC cannot see how the pointer is used (only as
an identifier), it cannot tell that the object doesn't need to be
initialized at that point at all. Work around this by using uintptr_t
instead.
PiperOrigin-RevId: 452380347
Change-Id: Ia5a493057ed90719de1d0efab71de9a8a08ddf8b