Add LLD_UNSAFE to force use of ld.bfd when ld is lld
By default the compiler will find /usr/bin/ld for the linker. If a port
sets LLD_UNSAFE and /usr/bin/ld is ld.lld, then add -fuse-ld=bfd to
force the use of the binutils BFD linker (from the base system, if
available, or by setting USE_BINUTILS).
This change is based on an earlier, similar patch from bapt, with the
addition of the -fuse-ld flag.