Split AndroidRuntime into AndroidRuntimeBase base-class and the rest.

AndroidRuntimeBase (exported by libandroid_runtime_base.so) is all you need
to link against to gain the ability to do AndroidRuntimeBase::getJNIEnv()
thus minimizing build dependencies.

Change-Id: Ia7f0c94c8c02b974c068e0db34774827f96aa95b
diff --git a/native/android/Android.mk b/native/android/Android.mk
index cda38e0..f55f94a 100644
--- a/native/android/Android.mk
+++ b/native/android/Android.mk
@@ -25,7 +25,8 @@
     libbinder \
     libui \
     libgui \
-    libandroid_runtime
+    libandroid_runtime \
+    libandroid_runtime_derived
 
 LOCAL_STATIC_LIBRARIES := \
     libstorage