Update DtoConstFP() to be correct after LLVM r67562, which changed the way the APFloat constructor expects its i80 APInts to be formatted. (They're now actually consistent with the x87 format)

// bug #191

int[3] a = [0: 0, 2: 42, 1: 1];

void main()
{
  assert(a[0] == 0);
  assert(a[1] == 1); // fails!
  assert(a[2] == 42);
}