[wasm] Do the default int64-lowering for all non-i64 stores.

First issue I found with my local fuzzing.

R=titzer@chromium.org
BUG=v8:5884

Review-Url: https://codereview.chromium.org/2656563003
Cr-Commit-Position: refs/heads/master@{#42683}

src/compiler/int64-lowering.cc

@@ -237,9 +237,7 @@ void Int64Lowering::LowerNode(Node* node) {
         NodeProperties::ChangeOp(node, store_op);
         ReplaceNode(node, node, high_node);
       } else {
-        if (HasReplacementLow(node->InputAt(2))) {
-          node->ReplaceInput(2, GetReplacementLow(node->InputAt(2)));
-        }
+        DefaultLowering(node);
       }
       break;
     }

test/mjsunit/regress/wasm/regression-5884.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.
+
+load('test/mjsunit/wasm/wasm-constants.js');
+load('test/mjsunit/wasm/wasm-module-builder.js');
+
+(function() {
+  var builder = new WasmModuleBuilder();
+  builder.addMemory(31, 31, false);
+  builder.addFunction('test', kSig_i_iii)
+      .addBodyWithEnd([
+        // body:
+        kExprI64Const, 0x41, kExprI64Const, 0x41, kExprI64LtS, kExprI32Const,
+        0x01, kExprI32StoreMem, 0x00, 0x41, kExprUnreachable,
+        kExprEnd,  // @60
+      ])
+      .exportFunc();
+  var module = builder.instantiate();
+})();