[Truffle] Fix n-body.

Author: chrisseaton

truffle/src/main/java/org/jruby/truffle/nodes/core/IONodes.java

@@ -92,10 +92,9 @@ public WriteNode(WriteNode prev) {
             return ToSNodeFactory.create(getContext(), getSourceSection(), other);
         }
 
+        @CompilerDirectives.TruffleBoundary
         @Specialization
         public int write(RubyString string) {
-            notDesignedForCompilation();
-
             final ByteList byteList = string.getByteList();
 
             final int offset = byteList.getBegin();