I'm working on switching to LLVM's lld linker as the FreeBSD system linker (/usr/bin/ld), and the port in this PR is reported as a new failure in the exp-run, PR 214864.
An excerpt from the build log:
ld: error: unable to find library -lm
ld: error: unable to find library -ldl
Known issues in this port or in lld that affect this port:
(2) 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.
FreeBSD 11 and later have lld available as /usr/bin/ld.lld, so one simple option for testing is to just symlink /usr/bin/ld to ld.lld (and restore it to ld.bfd).
A port Makefile knob, LLD_UNSAFE=yes, exists to indicate that a port does not work with lld, and requires either /usr/bin/ld.bfd or binutils from ports. This should work for the common case of ports written in C using GNU autoconf; it may have no effect on other ports.
Committed (with wrong PR in message) in r465752