We need to rebuild objfiles.txt when one of the subdirectories' objfiles.txt

changed in case a new file got added.

src/backend/common.mk

 #
 # Common make rules for backend
 #
-# $PostgreSQL: pgsql/src/backend/common.mk,v 1.6 2008/02/29 10:34:51 petere Exp $
+# $PostgreSQL: pgsql/src/backend/common.mk,v 1.7 2008/03/17 18:24:56 petere Exp $
 #
 
 # When including this file, set OBJS to the object files created in
@@ -27,8 +27,8 @@ SUBSYS.o: $(SUBDIROBJS) $(OBJS)
 	$(LD) $(LDREL) $(LDOUT) $@ $^
 
 objfiles.txt: Makefile $(SUBDIROBJS) $(OBJS)
-# Only rebuild the list if it does not exist or the Makefile has changed.
-	$(if $(filter $<,$?),( $(if $(SUBDIROBJS),cat $(SUBDIROBJS); )echo $(addprefix $(subdir)/,$(OBJS)) ) >$@,touch $@)
+# Don't rebuild the list if only the OBJS have changed.
+	$(if $(filter-out $(OBJS),$?),( $(if $(SUBDIROBJS),cat $(SUBDIROBJS); )echo $(addprefix $(subdir)/,$(OBJS)) ) >$@,touch $@)
 
 # make function to expand objfiles.txt contents
 expand_subsys = $(foreach file,$(1),$(if $(filter %/objfiles.txt,$(file)),$(patsubst ../../src/backend/%,%,$(addprefix $(top_builddir)/,$(shell cat $(file)))),$(file)))