Add support for overriding default Java libraries on a per-target basis

Change-Id: I425041554867a7ed7d74e1d603f160b2110bc86b
diff --git a/core/java.mk b/core/java.mk
index c7e93b7..2d9f1fb 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -43,7 +43,10 @@
   endif
 else
   ifneq ($(LOCAL_NO_STANDARD_LIBRARIES),true)
-    LOCAL_JAVA_LIBRARIES := core core-junit ext framework framework2 $(LOCAL_JAVA_LIBRARIES)
+    ifeq (TARGET_DEFAULT_JAVA_LIBRARIES,)
+      TARGET_DEFAULT_JAVA_LIBRARIES := core core-junit ext framework framework2
+    endif
+    LOCAL_JAVA_LIBRARIES := $(TARGET_DEFAULT_JAVA_LIBRARIES) $(LOCAL_JAVA_LIBRARIES)
   endif
 endif