tc: fix parallel build file with lex/yacc

Building iproute2 in parallel might hit the race failure:
	emp_ematch.l:2:30: fatal error: emp_ematch.yacc.h:
		No such file or directory
	make[1]: *** [emp_ematch.lex.o] Error 1

This is because we currently allow the yacc/lex files to generate and
compile in parallel.  So add a simple dependency to make sure yacc has
finished before we attempt to compile the lex output.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

tc/Makefile

@@ -136,6 +136,11 @@ m_xt_old.so: m_xt_old.c
 %.lex.c: %.l
 	$(LEX) $(LEXFLAGS) -o$@ $<
 
+# our lexer includes the header from yacc, so make sure
+# we don't attempt to compile it before the header has
+# been generated as part of the yacc step.
+emp_ematch.lex.o: emp_ematch.yacc.c
+
 ifneq ($(SHARED_LIBS),y)
 
 tc: static-syms.o