This fixes ocaml on non-x86 architectures, where we have code
that looks like:
#define Fl_head ((uintptr_t)(&sentinel.first_field))
Without this change, we get an error about a non-constant
initializer. This change takes the checks for pointers and
makes them apply to all expressions. It also makes the checks
stricter, preventing the following from compiling to junk:
int x;
int y = 42;
int *p = &x + y