[wasm] Fix empty asm.js function in ASM->WASM.

test/mjsunit/wasm/asm-wasm.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-wasm
 
+function EmptyTest() {
+  "use asm";
+  function caller() {
+    empty();
+    return 11;
+  }
+  function empty() {
+  }
+  return {caller: caller};
+}
+
+assertEquals(11, WASM.asmCompileRun(EmptyTest.toString()));
+
 function IntTest() {
   "use asm";
   function sum(a, b) {
     a = a|0;
     b = b|0;
     var c = (b + 1)|0
     return (a + c + 1)|0;
   }
 
   function caller() {
@@ skipping 718 matching lines @@
       }
       default: return 0;
     }
     return 0;
   }
 
   return {caller:caller};
 }
 
 assertEquals(43, WASM.asmCompileRun(TestNestedSwitch.toString()));