core: Add a phony package definition

This allows one to declare a meta-package that depends on a list
of modules. This is extremely useful for vendor provided prebulit
libraries where there is a big list of libraries/binaries to include.
Specifying that list in multiple places would be error prone and
eventually lead to very annoying bug hunts.

With a fake package, one does:

LOCAL_MODULE := my_fake_package
LOCAL_REQUIRED_MODULES := <list of required module names>
LOCAL_MODULE_TAGS := optional
include $(BUILD_PHONY_PACKAGE)

Change-Id: Idcfe91f6f2d6d886aba094981a70690e5a808bfc
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/core/config.mk b/core/config.mk
index b283b8c..51a5d9c 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -61,6 +61,7 @@
 BUILD_RAW_EXECUTABLE:= $(BUILD_SYSTEM)/raw_executable.mk
 BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk
 BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk
+BUILD_PHONY_PACKAGE:= $(BUILD_SYSTEM)/phony_package.mk
 BUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mk
 BUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mk
 BUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mk