Merge pull request lh3#27 from junghans/fix_parallel_build

fixed parallel build

makefile

@@ -54,10 +54,15 @@ a.out:	ytab.o $(OFILES)
 
 $(OFILES):	awk.h ytab.h proto.h
 
-ytab.c:	awk.h proto.h awkgram.y
+#Clear dependency for parallel build: (make -j)
+#YACC generated y.tab.c and y.tab.h at the same time
+#this needs to be a static pattern rules otherwise multiple target
+#are mapped onto multiple executions of yacc, which overwrite 
+#each others outputs.
+y%.c y%.h:	awk.h proto.h awkgram.y
 	$(YACC) $(YFLAGS) awkgram.y
-	mv y.tab.c ytab.c
-	mv y.tab.h ytab.h
+	mv y.$*.c y$*.c
+	mv y.$*.h y$*.h
 
 ytab.h:	ytab.c