Use LDFLAGS.
--- src/Makefile.in.orig	2010-03-01 15:13:17.000000000 -0600
+++ src/Makefile.in	2021-07-29 11:44:40.000000000 -0500
@@ -65,7 +65,7 @@
 	ar -cr $@ $(OBJS)
 	$(RANLIB) $@
 $(LIBSHARED): $(OBJS_SHARED)
-	$(CC) -shared -Wl,-soname,$(LIBSHARED) -o $(LIBSHARED) $(OBJS_SHARED) $(LIBS) $(LNETLIB) $(PCAPLIB)
+	$(CC) -shared -Wl,-soname,$(LIBSHARED) -o $(LIBSHARED) $(OBJS_SHARED) $(LDFLAGS) $(LIBS) $(LNETLIB) $(PCAPLIB)
 
 _install install: $(LIBSTATIC)
 	../mkinstalldirs $(install_prefix)$(libdir)