[ARITH] Avoid imaxdiv when only one of the results is wanted

[ARITH] Avoid imaxdiv when only one of the results is wanted

dash rather pointlessly calls imaxdiv, only to discard one of its
results. The call was already made conditional a while back because some
systems don't have imaxdiv, but the generated code for the version with
imaxdiv and the one with / and % is identical (with GCC 4.6.1 or ICC
12.0.2, with -O0, -O2 or -Os), so it could just as well go entirely to
clean up the code a little bit.

Signed-off-by: Harald van Dijk <harald@gigawatt.nl>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>