Add build rules to generate native DBus interfaces

With this patch, we can now write Android makefiles like:

include $(CLEAR_VARS)
LOCAL_MODULE := dbus-binding-example
LOCAL_SRC_FILES := main.cpp \
                   dbus-service-config.json \
                   org.example.Daemon.Command.dbus.xml \
                   org.example.Daemon.Manager.dbus.xml
include $(BUILD_EXECUTABLE)

This will cause header files defining native DBus interfaces
to be generated.  These can be included from main.cpp to
easily expose object oriented interface over DBus.

Bug: 22608897
Change-Id: Ic4304ac8de77de74d6955ed17789e5477be9a53e
diff --git a/core/config.mk b/core/config.mk
index 882ab0c..fec018b 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -399,6 +399,7 @@
 AAPT := $(HOST_OUT_EXECUTABLES)/aapt$(HOST_EXECUTABLE_SUFFIX)
 AIDL := $(HOST_OUT_EXECUTABLES)/aidl$(HOST_EXECUTABLE_SUFFIX)
 PROTOC := $(HOST_OUT_EXECUTABLES)/aprotoc$(HOST_EXECUTABLE_SUFFIX)
+DBUS_GENERATOR := $(HOST_OUT_EXECUTABLES)/dbus-binding-generator
 SIGNAPK_JAR := $(HOST_OUT_JAVA_LIBRARIES)/signapk$(COMMON_JAVA_PACKAGE_SUFFIX)
 MKBOOTFS := $(HOST_OUT_EXECUTABLES)/mkbootfs$(HOST_EXECUTABLE_SUFFIX)
 MINIGZIP := $(HOST_OUT_EXECUTABLES)/minigzip$(HOST_EXECUTABLE_SUFFIX)