audio/alure: set LLD_UNSAFE

Linking with LLD currently fails due to preemption of symbols with
protected visibility in a shared object:

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

defined in libalure.so.1.2.0
referenced by examples/alurestream.c

CMakeFiles/alurestream.dir/examples/alurestream.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 openal-soft or in lld).

PR: 214864, 219089
Approved by: portmgr (LLD_UNSAFE blanket)
Sponsored by: The FreeBSD Foundation