[wasm] Rename the WASM object to _WASMEXP_.

test/mjsunit/wasm/compile-run-basic.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
 
 load("test/mjsunit/wasm/wasm-constants.js");
 
 var kReturnValue = 97;
 
@@ skipping 10 matching lines @@
   0, 0,                       // signature index
   kNameOffset, 0, 0, 0,       // name offset
   kBodySize, 0,               // body size
   // -- body
   kExprI8Const,               // --
   kReturnValue,               // --
   kDeclEnd,
   'm', 'a', 'i', 'n', 0       // name
 );
 
-assertEquals(kReturnValue, WASM.compileRun(data));
+assertEquals(kReturnValue, _WASMEXP_.compileRun(data));