In *-*-user/ build dirs CONFIG_USER_ONLY is defined via config-target.h.
In libuser/ it is not defined.
Add it via QEMU_CFLAGS.
Signed-off-by: Andreas Färber <afaerber@suse.de> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>