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_System.cc b/runtime/native/java_lang_System.cc
index 43681a7..f79be56 100644
--- a/runtime/native/java_lang_System.cc
+++ b/runtime/native/java_lang_System.cc
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include "java_lang_System.h"
+
 #include "common_throws.h"
 #include "gc/accounting/card_table-inl.h"
 #include "jni_internal.h"