6631003: Add hg tip changeset to build image

Reviewed-by: mduigou

.hgignore

@@ -2,3 +2,4 @@
 ^dist/
 /nbproject/private/
 ^webrev
+^.hgtip

Makefile

@@ -97,7 +97,7 @@ define StopTimer
 endef
 
 # Generic build of basic repo series
-generic_build_repo_series::
+generic_build_repo_series:: $(SOURCE_TIPS)
 	$(MKDIR) -p $(OUTPUTDIR)
 	$(MKDIR) -p $(OUTPUTDIR)/j2sdk-image
 	@$(call StartTimer)
@@ -243,6 +243,14 @@ product_build:: build_product_image
 debug_build:: build_debug_image
 fastdebug_build:: build_fastdebug_image
 
+# The source tips are stored with the relative path to the repo.
+#   This file will be used when constructing the jdk image.
+source_tips: $(SOURCE_TIPS)
+	$(CAT) $<
+$(SOURCE_TIPS): FRC
+	@$(prep-target)
+	@$(call GetSourceTips)
+
 clobber:: REPORT_BUILD_TIMES=
 clobber:: 
 	$(RM) -r $(OUTPUTDIR)/*