Use prebuilt for PDK builds.

Change-Id: Ief723fe137b7a3aa051837e3ca1079fea772357d
diff --git a/tools/Android.mk b/tools/Android.mk
index d6badab..a29cd3d 100644
--- a/tools/Android.mk
+++ b/tools/Android.mk
@@ -14,7 +14,7 @@
 # limitations under the License.
 #
 
-ifeq ($(TARGET_BUILD_APPS),)
+ifeq (,$(TARGET_BUILD_APPS)$(filter true,$(TARGET_BUILD_PDK)))
 LOCAL_PATH := $(call my-dir)
 include $(call first-makefiles-under,$(LOCAL_PATH))
 endif