https://bugs.gentoo.org/511892

the scanner needs the generated header file, so make sure it's listed as a
dependency.  else you see a failure:
	$ cd sfbpf
	$ make clean
	$ make sf_scanner.lo
	<missing tokdefs.h>
we'd like to list it as a dep of the object, but automake can use generated
file names, so it's not easy to list that.

we can't have both of the outputs from grammar.y run the lex, otherwise we
hit random parallel build failures:
	$ cd sfbpf
	$ make clean
	$ make tokdefs.h sf_grammar.c -j
	<run yacc twice & fail>

--- a/sfbpf/Makefile.am
+++ b/sfbpf/Makefile.am
@@ -43,14 +43,16 @@
 libsfbpf_la_LDFLAGS = -version-info 0:1:0 @XCCFLAGS@
 
 # use of $@ and $< here is a GNU idiom that borks BSD
-${builddir}/sf_scanner.c: ${srcdir}/scanner.l
+${builddir}/sf_scanner.c: ${srcdir}/scanner.l ${builddir}/tokdefs.h
 	@rm -f ${builddir}/sf_scanner.c
 	${srcdir}/runlex.sh $(V_LEX) -osf_scanner.c ${srcdir}/scanner.l
 
-${builddir}/tokdefs.h ${builddir}/sf_grammar.c: ${srcdir}/grammar.y
+${builddir}/sf_grammar.c: ${srcdir}/grammar.y
 	@rm -f ${builddir}/sf_grammar.c ${builddir}/tokdefs.h
 	$(V_YACC) -d ${srcdir}/grammar.y
 	mv y.tab.c sf_grammar.c
 	mv y.tab.h tokdefs.h
 
+${builddir}/tokdefs.h: ${builddir}/sf_grammar.c ; @true
+
 CLEANFILES = ${builddir}/sf_scanner.c ${builddir}/sf_grammar.c ${builddir}/tokdefs.h ${builddir}/sf_scanner.h