Include libffi in executable.

Makefile

@@ -9,7 +9,7 @@ OFLAGS += $(GFLAGS) -O3 -DNDEBUG -DTYPECODES=1 -DDELOPT=1
 PFLAGS += $(OFLAGS) -pg
 CFLAGS += -D_GNU_SOURCE -I/opt/local/include
 LDLIBS += -L/opt/local/lib
-LDLIBS += -lgc -lm
+LDLIBS += -lgc -lm -lffi
 
 MAIN = minproto