egcs-2.91-66 generates the following warning on this code:
[root@chameleon Linux]# gcc -o foo foo.c
foo.c: In function `main':
foo.c:6: warning: comparison is always 0 due to limited range of data type

int
main(int argc, char **argv)
{
  int rc = 0;
  char c = 0xa5, *ptr=&c;
  if (*ptr == 0xa5) rc = 1; /* This is the line that generates the warning
*/
  return rc;
}