Fix build

Change-Id: I5fc25cf89ce23fe22691d5146488d874e1d93acc
diff --git a/tests/tests/mediastress/jni/Android.mk b/tests/tests/mediastress/jni/Android.mk
index 3913b54..26ff647 100644
--- a/tests/tests/mediastress/jni/Android.mk
+++ b/tests/tests/mediastress/jni/Android.mk
@@ -24,7 +24,7 @@
 
 LOCAL_C_INCLUDES := $(JNI_H_INCLUDE)
 
-LOCAL_CFLAGS += -Isystem/media/wilhelm/include
+LOCAL_C_INCLUDES += $(call include-path-for, wilhelm)
 
 LOCAL_SHARED_LIBRARIES := libandroid libnativehelper liblog libOpenMAXAL