y2038: Use a common definition for msqid_ds

y2038: Use a common definition for msqid_ds

Instead of replicate the same definitions from struct_msqid64_ds.h
on the multiple struct_msqid_ds.h, use a common header which is included
when required (struct_msqid64_ds_helper.h).

The __USE_TIME_BITS64 is not defined internally yet, although the
internal header is used when building the 64-bit stat implementations.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>