page pointers portable to 32bit platforms

[comotion]

Use the appropriate pointer type uintptr_t.

A 32bit build will fail with the following error due to -Werror:

core/memory.c: In function 'virtual_to_physical':
core/memory.c:36:16: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
   virt_page = ((uint64_t)ptr) / 4096;
                ^
...
core/memory.c:51:5: error: format '%lx' expects argument of type 'long unsigned int', but argument 4 has type 'uint64_t' [-Werror=format=]
core/memory.c: In function 'allocate_huge_page':
core/memory.c:93:26: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   realptr = shmat(shmid, (void*)virtual_address, 0);
                          ^

This patch is split out from #483, and fixes the problem by using an int type that changes size with the page size.

[eugeneia]

I am merging this into max-next as its a change regarding general correctness of C code.

Cc @lukego