Adapt sim to new version number & date locations.

Adapt sim to new version number & date locations.

This change is required now that gdb/version.in has been moved to
gdb/common/version.in and now that the date needs to be fetched
from bfd/version.h.

sim/common/ChangeLog:

        * create-version.sh: New script. Adapted from
        gdb/commong/create-version.sh.
        * Make-common.in (version.c): Update rule dependencies,
        and re-implement using create-version.sh.

sim/ppc/ChangeLog:

        * Makefile.in (srccom): New variable.
        (version.c): Update rule dependencies, and re-implement using
        sim/common/create-version.sh.