Allow several system property files

TARGET_SYSTEM_PROP now is a list of files and all of them
are included in the build.prop.

Change-Id: I494f86412b0a299ee4c066e49ab4f4686bc2178a
diff --git a/core/Makefile b/core/Makefile
index 507a198..70598ae 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -190,9 +190,14 @@
 			TARGET_CPU_ABI2="$(TARGET_CPU_ABI2)" \
 			TARGET_AAPT_CHARACTERISTICS="$(TARGET_AAPT_CHARACTERISTICS)" \
 	        bash $(BUILDINFO_SH) > $@
-	$(hide) if [ -f "$(system_prop_file)" ]; then \
-	          cat $(system_prop_file) >> $@; \
-	        fi
+	$(hide) $(foreach file,$(system_prop_file), \
+		if [ -f "$(file)" ]; then \
+			echo "#" >> $@; \
+			echo Target buildinfo from: "$(file)"; \
+			echo "# from $(file)" >> $@; \
+			echo "#" >> $@; \
+			cat $(file) >> $@; \
+		fi;)
 	$(if $(ADDITIONAL_BUILD_PROPERTIES), \
 		$(hide) echo >> $@; \
 		        echo "#" >> $@; \