% and REM fail to handle -1, -9223372036854775808

[Sejsel]

Currently, both % and REM instructions will fail with IntegerOverflow when used with -1, -9223372036854775808 as the parameters, even though the result should clearly be zero.

This happens because the rust checked_rem_euclid and checked_rem both "overflow" on this case. It is documented (with no explanation given, and to be honest, when I looked up the design of these functions, it doesn't exactly look like it was given much thought). It is clearly wrong from the viewpoint of the result.

-9223372036854775804         mod -1 = 0
-9223372036854775804 checked mod -1 = Some(0)
-9223372036854775805         mod -1 = 0
-9223372036854775805 checked mod -1 = Some(0)
-9223372036854775806         mod -1 = 0
-9223372036854775806 checked mod -1 = Some(0)
-9223372036854775807         mod -1 = 0
-9223372036854775807 checked mod -1 = Some(0)
-9223372036854775808         mod -1 = 0
-9223372036854775808 checked mod -1 = None

We do have tests checking this case (they expect fail), but we should change them to expect 0 as the result.