Make common scanner fill function, as we're using it in two places already.

Make common scanner fill function, as we're using it in two places already.
Actually, GAS parser doesn't use this yet, as it still contains the rept
functionality that will move to GAS preproc at some point.  When GAS
preproc implements rept, we can switch to the common implementation.

svn path=/trunk/yasm/; revision=1668