new loop c-torture test

[Joern Rennecke]

This fails at -O2 for x86; it's slightly modified from loop-4.c to
trigger an overflow to positive in check_dbra_loop.

I think we should also have an existing problem with loop-4.c when
cross-compiling from a 64 bit host to a 32 bit target.

int
f()
{
  int j = 1;
  long i;
  i = 0x60000000L;
  do
    {
      j <<= 1;
      i += 0x10000000L;
    } while (i < -0x60000000L);
  return j;
}

int
main ()
{
  if (f () != 2)
    abort ();
  exit (0);
}