Compile arch specific GCM implementations only on target arch
* cipher/Makefile.am: Move arch specific 'cipher-gcm-*.[cS]' files from libcipher_la_SOURCES to EXTRA_libcipher_la_SOURCES. * configure.ac: Add 'cipher-gcm-intel-pclmul.lo' and 'cipher-gcm-arm*.lo'.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>