target-mips: optimize ddiv/ddivu/div/divu with movcond

The result of a division by 0, or a division of INT_MIN by -1 in the
signed case, is unpredictable. Just replace 0 by 1 in that case so that
it doesn't trigger a floating point exception on the host.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
