Syntax clean up to make clang happy.

Change-Id: I0984c395bbd1ee4b206eafd19915b6f68781dd16
diff --git a/src/runtime.h b/src/runtime.h
index 3b9919c..f613991 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -47,7 +47,7 @@
 class DexFile;
 class Heap;
 class InternTable;
-class JavaVMExt;
+struct JavaVMExt;
 class Method;
 class MonitorList;
 class SignalCatcher;