Do not build poly1305-s390x.S on foreign architectures
* configure.ac [host=s390x-*-*]: Add 'poly1305-s390x.lo'. * cipher/Makefile.am: Move 'poly1305-s390x.S' to 'EXTRA_libcipher_la_SOURCES'.
- GnuPG-bug-id: T5694
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>