[wasm] Provide backoff implementations for the Fxx rounding instructions

test/cctest/test-api-fast-accessor-builder.cc

 // 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.
 
 #include <stdlib.h>
 
 #include "include/v8.h"
 #include "include/v8-experimental.h"
 
 #include "src/api.h"
@@ skipping 269 matching lines @@
   val.intval = 0;
   ExpectInt32("nonzero()", 0);
   val.intval = 27;
   ExpectInt32("nonzero()", 1);
 
   // Access val.v8val:
   CompileRun(FN_WARMUP("loadval", "return obj.loadval"));
   ExpectString("loadval()", "Hello");
 }
 
-
 void ApiCallbackInt(const v8::FunctionCallbackInfo<v8::Value>& info) {
   info.GetReturnValue().Set(12345);
 }
 
 const char* kApiCallbackStringValue =
     "Hello World! Bizarro C++ world, actually.";
 void ApiCallbackString(const v8::FunctionCallbackInfo<v8::Value>& info) {
   info.GetReturnValue().Set(v8_str(kApiCallbackStringValue));
 }
 
-
 void ApiCallbackParam(const v8::FunctionCallbackInfo<v8::Value>& info) {
   CHECK_EQ(1, info.Length());
   CHECK(info[0]->IsNumber());
   info.GetReturnValue().Set(info[0]);
 }
 
-
 // "Fast" accessor, callback to embedder
 TEST(FastAccessorCallback) {
   LocalContext env;
   v8::Isolate* isolate = env->GetIsolate();
   v8::HandleScope scope(isolate);
 
   v8::Local<v8::ObjectTemplate> foo = v8::ObjectTemplate::New(isolate);
   {
     auto builder = v8::experimental::FastAccessorBuilder::New(isolate);
     builder->ReturnValue(
@@ skipping 24 matching lines @@
   // Callbacks:
   CompileRun(FN_WARMUP("callbackint", "return obj.int"));
   ExpectInt32("callbackint()", 12345);
 
   CompileRun(FN_WARMUP("callbackstr", "return obj.str"));
   ExpectString("callbackstr()", kApiCallbackStringValue);
 
   CompileRun(FN_WARMUP("callbackparam", "return obj.param"));
   ExpectInt32("callbackparam()", 1000);
 }