multimedia/libxine: set LLD_UNSAFE to avoid lld

libxine relies on ld.bfd's permissive treatment of shared library
symbols with protected visibility, and attempting to link with lld
fails with errors like:

/usr/bin/ld: error: cannot preempt symbol: xine_get_version_string

defined in ../src/xine-engine/.libs/libxine.so
referenced by xine-list.c:98

xine-list.o:(main)

For now set LLD_UNSAFE=yes so that the port will continue to link with
ld.bfd if /usr/bin/ld is lld, until the issue can be addressed (with a
change in libxine or in lld).

PR: 214864
Approved by: portmgr (LLD_UNSAFE blanket)
Sponsored by: The FreeBSD Foundation