This changes the API of xfa from
XFA(array_name, prio) type element_name = INITIALIZER;
to
XFA(type, array_name, prio) element_name = INITIALIZER;
this allows forcing natural alignment of the type, fixing failing tests
on `native64`.
Use `uintptr_t` for arithmetic rather than `const char *` to fix the
following warning:
> comparePointers: Subtracting pointers that point to different objects