In the unit tests, use "test_eq_ptr" and "test_neq_ptr" consistently

In the unit tests, use "test_eq_ptr" and "test_neq_ptr" consistently

This is part of what's needed to build without warnings on mingw64:
it was warning about the cast from void* to long that happened in
the places we were using test_{n,}eq on pointers.

The alternative here would have been to broaden tt_int_op to accept
a long long or an intptr_t, but that's less correct (since pointers
aren't integers), and would hurt the portability of tinytest a
little.

Fixes part of 7260.