Avoid more GCC warnings in the runtime on 64-bit Windows.

runtime/mercury_ml_expand_body.h:
	Fix another spot where we are incorrectly assuming that
	the machine word size is <= sizeof(long).

runtime/mercury_debug.c:
runtime/mercury_memory_zones.c:
runtime/mercury_wrapper.c:
	s/MR_WORD_TYPE/MR_Integer/ in my last change.