Fix DSL warning.

(cherry picked from commit e4702fb)

Author: woess

graal-js/src/com.oracle.truffle.js/src/com/oracle/truffle/js/builtins/IteratorHelperPrototypeBuiltins.java

@@ -42,6 +42,7 @@
 
 import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.dsl.Cached;
+import com.oracle.truffle.api.dsl.Cached.Exclusive;
 import com.oracle.truffle.api.dsl.Cached.Shared;
 import com.oracle.truffle.api.dsl.ImportStatic;
 import com.oracle.truffle.api.dsl.Specialization;
@@ -136,7 +137,7 @@ public Object suspendedStart(VirtualFrame frame, JSIteratorHelperObject thisObj,
         @Specialization(guards = {"thisObj.getGeneratorState() == SuspendedYield"})
         public Object suspendedYield(VirtualFrame frame, JSIteratorHelperObject thisObj,
                         @Cached("create(getContext())") @Shared IteratorCloseNode outerIteratorCloseNode,
-                        @Cached("create(getContext())") IteratorCloseNode innerIteratorCloseNode) {
+                        @Cached("create(getContext())") @Exclusive IteratorCloseNode innerIteratorCloseNode) {
             thisObj.setGeneratorState(JSFunction.GeneratorState.Executing);
 
             try {