ART: More warnings

Enable -Wno-conversion-null, -Wredundant-decls and -Wshadow in general,
and -Wunused-but-set-parameter for GCC builds.

Change-Id: I81bbdd762213444673c65d85edae594a523836e5
diff --git a/runtime/native/java_lang_ref_Reference.cc b/runtime/native/java_lang_ref_Reference.cc
index 4f04d60..d232059 100644
--- a/runtime/native/java_lang_ref_Reference.cc
+++ b/runtime/native/java_lang_ref_Reference.cc
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include "java_lang_ref_Reference.h"
+
 #include "gc/heap.h"
 #include "gc/reference_processor.h"
 #include "jni_internal.h"