multimedia/xine: set LLD_UNSAFE to avoid lld

xine 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_usec_sleep

defined in /usr/local/lib/libxine.so
referenced by actions.c

actions.o:(wait_for_window_visible)

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