devel/libds: use BINARY_ALIAS to ensure linker is ld.bfd

lld has no built-in search paths (/lib, /usr/lib). Normally the linker
is invoked from the compiler driver, and the search paths are added by
the compiler. If lld is invoked directly library search paths must be
specified explicitly, with -L/lib -L/usr/lib.

This port does not honour LD or -fuse-ld in CFLAGS via LLD_UNSAFE, but
BINARY_ALIAS can be used to ensure we use the BFD linker.

PR: 226972
Approved by: portmgr (LLD_UNSAFE blanket)
Sponsored by: The FreeBSD Foundation