[wasm] Do not patch memory references in imported functions.

test/mjsunit/regress/wasm/regress-5860.js

+// Copyright 2017 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');
+load('test/mjsunit/wasm/wasm-module-builder.js');
+
+let module1 = (() => {
+  let builder = new WasmModuleBuilder();
+  builder.addMemory(1, 1);
+  builder.addFunction('load', kSig_i_i)
+      .addBody([kExprI32Const, 0, kExprI32LoadMem, 0, 0])
+      .exportAs('load');
+  return new WebAssembly.Module(builder.toBuffer());
+})();
+
+let module2 = (() => {
+  let builder = new WasmModuleBuilder();
+  builder.addMemory(1, 1);
+  builder.addImport('A', 'load', kSig_i_i);
+  builder.addExportOfKind('load', kExternalFunction, 0);
+  return new WebAssembly.Module(builder.toBuffer());
+})();
+
+let instance1 = new WebAssembly.Instance(module1);
+let instance2 = new WebAssembly.Instance(module2, {A: instance1.exports});
+
+assertEquals(0, instance2.exports.load());