hppa: Fix warnings from _dl_lookup_address

This change fixes two warnings from _dl_lookup_address.

The first warning comes from dropping the volatile keyword from
desc in the call to _dl_read_access_allowed.  We now have a full
atomic barrier between loading desc[0] and the access check, so
desc no longer needs to be declared as volatile.

The second warning comes from the implicit declaration of
_dl_fix_reloc_arg.  This is fixed by including dl-runtime.h and
declaring _dl_fix_reloc_arg in dl-runtime.h.