Allow multiple directories in LOCAL_RESOURCE_DIR

Before, LOCAL_RESOURCE_DIR got messed up when the build system
tried to find the whole LOCAL_RESOURCE_DIR string in each
overlay directory.

This change splits LOCAL_RESOURCE_DIR before appending it to
the overlay directory paths.

I've verified that this now works:

LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/overlay $(LOCAL_PATH)/res

Change-Id: Iea47f94a14720af0ca4b422aec30acf4acbe13cf
diff --git a/core/package.mk b/core/package.mk
index 70f10e0..2ee3996 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -69,8 +69,10 @@
   LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
 endif
 LOCAL_RESOURCE_DIR := \
-  $(wildcard $(addsuffix /$(LOCAL_RESOURCE_DIR), $(PRODUCT_PACKAGE_OVERLAYS))) \
-  $(wildcard $(addsuffix /$(LOCAL_RESOURCE_DIR), $(DEVICE_PACKAGE_OVERLAYS))) \
+  $(wildcard $(foreach dir, $(PRODUCT_PACKAGE_OVERLAYS), \
+    $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \
+  $(wildcard $(foreach dir, $(DEVICE_PACKAGE_OVERLAYS), \
+    $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \
   $(LOCAL_RESOURCE_DIR)
 
 # this is an app, so add the system libraries to the search path