It seems at least some versions of g++ don't support -rpath.

3e18baaa · deuce · a216d5cf · 3e18baaa
Commit 3e18baaa authored 5 years ago by deuce
--- a/src/sbbs3/GNUmakefile
+++ b/src/sbbs3/GNUmakefile
@@ -84,7 +84,6 @@ else
 endif
 endif
 export LD_RUN_PATH
-LDFLAGS += -rpath $(LD_RUN_PATH)

 CON_LIBS	+= -lsbbs -lftpsrvr -lwebsrvr -lmailsrvr -lservices
 SHLIBOPTS	:=	-shared