Fix intermittent parallel build failure
https://trac.macports.org/ticket/45159
--- sfbpf/Makefile.in.orig	2015-04-23 10:19:16.000000000 -0500
+++ sfbpf/Makefile.in	2015-05-20 09:11:52.000000000 -0500
@@ -776,7 +776,7 @@
 
 
 # use of $@ and $< here is a GNU idiom that borks BSD
-sf_scanner.c: $(srcdir)/scanner.l
+sf_scanner.c: $(srcdir)/scanner.l ${builddir}/tokdefs.h
 	@rm -f $(srcdir)/sf_scanner.c
 	$(srcdir)/runlex.sh $(V_LEX) -osf_scanner.c $(srcdir)/scanner.l