Support for unbundled app build

With this CL, run "make APP-{appname}" to build unbundled app in
the unbundled app src tree.
See http://b/issue?id=2667113

Change-Id: I1d753db795142508bc841ae66b4408220ab687c5
diff --git a/core/product.mk b/core/product.mk
index be32e9e..7594f6f 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -29,13 +29,13 @@
 endef
 
 #
-# Returns the sorted concatenation of all PRODUCT_MAKEFILES
-# variables set in all AndroidProducts.mk files.
-# $(call ) isn't necessary.
+# Returns the sorted concatenation of PRODUCT_MAKEFILES
+# variables set in the given AndroidProducts.mk files.
+# $(1): the list of AndroidProducts.mk files.
 #
-define get-all-product-makefiles
+define get-product-makefiles
 $(sort \
-  $(foreach f,$(_find-android-products-files), \
+  $(foreach f,$(1), \
     $(eval PRODUCT_MAKEFILES :=) \
     $(eval LOCAL_DIR := $(patsubst %/,%,$(dir $(f)))) \
     $(eval include $(f)) \
@@ -47,6 +47,15 @@
 endef
 
 #
+# Returns the sorted concatenation of all PRODUCT_MAKEFILES
+# variables set in all AndroidProducts.mk files.
+# $(call ) isn't necessary.
+#
+define get-all-product-makefiles
+$(call get-product-makefiles,$(_find-android-products-files))
+endef
+
+#
 # Functions for including product makefiles
 #