Some ports depend on permissive or broken behaviour from the GNU BFD linker, ld.bfd. Clang and GCC support a -fuse-ld= flag to specify the linker to use, and as we migrate to installing lld as the base system's /usr/bin/ld we'll want to make use of -fuse-ld=bfd to let ports that fail with lld use bfd instead.
An upstream libtool change from Feb 2016 supports passing through -fuse-ld=, but it has not yet made it into a release: http://git.savannah.gnu.org/cgit/libtool.git/commit/?id=f9970d99293faf908fdc153a653fa5781095fb7a
Patch an equivalent change into ltmain.sh via Mk/Uses/libtool.mk.
See PR 224514 for an earlier attempt which address this in the libtool port only, and so fixes those ports that have USES=autoreconf but not ports using their own ltmain.sh. @tijl suggested this change.