Add system/build.prop dependency on vendor/bootimg

When incremental builds only affect the system partition,
the build.prop file for other partitions might go out of
date.

Add a dependency on system/build.prop s.t. when
it's rebuilt,
the fingerprints are updated on the other
partition's build.prop's.

Bug:19058575
Change-Id: Iea7b761e0800c402eb4ce1154e8f6af5a17f7b06
diff --git a/core/Makefile b/core/Makefile
index 0d07423..6467570 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -270,7 +270,7 @@
 
 INSTALLED_BOOTIMAGE_BUILD_PROP_TARGET := $(TARGET_ROOT_OUT)/build.prop
 ALL_DEFAULT_INSTALLED_MODULES += $(INSTALLED_BOOTIMAGE_BUILD_PROP_TARGET)
-$(INSTALLED_BOOTIMAGE_BUILD_PROP_TARGET):
+$(INSTALLED_BOOTIMAGE_BUILD_PROP_TARGET): $(INSTALLED_BUILD_PROP_TARGET)
 	@echo Target bootimage buildinfo: $@
 	@mkdir -p $(dir $@)
 	$(hide) echo > $@