Derived from https://github.com/opencog/link-grammar/commit/8d864c6a7b91

--- configure.orig	2022-06-17 16:29:31 UTC
+++ configure
@@ -18540,8 +18540,26 @@ fi
   OS_NETBSD_FALSE=
 fi
 
+case "$host_os" in
+  *freebsd*)
+    freebsd=yes
+    ;;
+  *)
+    freebsd=no
+    ;;
+esac
 
 HOST_OS="$host_os"
+
+# ====================================================================
+# FreeBSD work-around. Apparently, the AX_PTHREAD autoconf macro
+# fails to include -lstdthreads in it's results. See bug report
+# https://github.com/opencog/link-grammar/issues/1355
+# So we hack, and explicitly set it here.
+
+if test -n "$ax_pthread_ok" -a "x$freebsd" = "xyes"; then
+	PTHREAD_LIBS="${PTHREAD_LIBS} -lstdthreads"
+fi
 
 # ====================================================================