[wasm] Fix double to int conversions.

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 IntTest() {
   "use asm";
   function sum(a, b) {
     a = a|0;
     b = b|0;
     var c = (b + 1)|0
+    var d = 3.0;
+    var e = d | 0;  // double conversion
     return (a + c + 1)|0;
   }
 
   function caller() {
     return sum(77,22) | 0;
   }
 
   return {caller: caller};
 }
 
@@ skipping 712 matching lines @@
       }
       default: return 0;
     }
     return 0;
   }
 
   return {caller:caller};
 }
 
 assertEquals(43, WASM.asmCompileRun(TestNestedSwitch.toString()));