chinese/libpinyin: Switch DB backend and improve port

• Switch to DISTVERSION
• Use GitHub as primary download site and Sourceforge as fallback
• Use USES= localbase:ldflags helper
• Switch from DBD5 (deprecated) to KyotoCabinet as backend
• Remove GNU_CONFIGURE_MANPREFIX

PR: 279124
Reviewed by: Zhihao Yuan <lichray@gmail.com> (maintainer)