Fix compiler warnings on 64-bit Windows

GCC reports various instances of

warning: cast to pointer from integer of different size
[-Wint-to-pointer-cast]
warning: cast from pointer to integer of different size
[-Wpointer-to-int-cast]

and MSVC equivalently

warning C4312: 'type cast': conversion from 'int' to 'void *' of
greater size
warning C4311: 'type cast': pointer truncation from 'void *' to 'long'

in ECPG test files. This is because void* and long are cast back and
forth, but on 64-bit Windows, these have different sizes. Fix by
using intptr_t instead.

The code actually worked fine because the integer values in use are
all small. So this is just to get the test code to compile warning-free.

--
Peter Eisentraut http://www.2ndQuadrant.com/
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