libhardware: add separate makefile for modules subdir

Change-Id: I787c444ee1c3a687ee6f8f551c359e5e908ed7f5
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/modules/hwcomposer/Android.mk b/modules/hwcomposer/Android.mk
index da2b234..f1e819b 100644
--- a/modules/hwcomposer/Android.mk
+++ b/modules/hwcomposer/Android.mk
@@ -24,4 +24,5 @@
 LOCAL_SRC_FILES := hwcomposer.cpp
 LOCAL_MODULE := hwcomposer.default
 LOCAL_CFLAGS:= -DLOG_TAG=\"hwcomposer\"
+LOCAL_MODULE_TAGS := optional
 include $(BUILD_SHARED_LIBRARY)