A couple of observations...

First off, you need to use 0x12345678L (note the L) to create a "long" constant; otherwise you may end up accidentally truncating it.

Second, the m32c is little-endian, so memory contents should be as follows (all hex):

200000  78

200001  56

200002  34

200004  12

If you look at them as 16-bit locations:

200000 5678

200002 1234

If you're not getting these values, it's time to check the hardware.  For 16-bit memory, make sure you did NOT use the A0 address line.  Also, double check your timing.  Try this program (assuming you have a suitable printf), first WITHOUT the pragma (to see how it should work), then WITH (to test the memory connections):

#include <stdio.h>

unsigned long x;

main()
{
  unsigned char *cp;
  int i;

  x = 0x12345678;
  cp = (unsigned char *)&x;
  for (i=0; i<4; i++)
    printf(" %02x", cp[i]);
  printf("\n");
}