audio/oss: set LLD_UNSAFE to link using ld.bfd

This port fails when attempting to link with lld as the system linker.
It passes -fPIC to the linker, which is actually a compiler flag.
ld.bfd accepts the flag but it results in a bogus DT_AUXILIARY entry
in the ouptut:

Dynamic section at offset 0x5000 contains 15 entries:

Tag                Type                  Name/Value

0x000000007ffffffd AUXILIARY Auxiliary library: [PIC]

PR: 221807
Approved by: portmgr (LLD_UNSAFE blanket)
Sponsored by: The FreeBSD Foundation