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

test/mjsunit/regress/wasm/regression-5884.js

Index: test/mjsunit/regress/wasm/regression-5884.js
diff --git a/test/mjsunit/regress/wasm/regression-5884.js b/test/mjsunit/regress/wasm/regression-5884.js
new file mode 100644
index 0000000000000000000000000000000000000000..8677f105eec4af715044b9d7c59a1837d44e917e
--- /dev/null
+++ b/test/mjsunit/regress/wasm/regression-5884.js
@@ -0,0 +1,20 @@
+// 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();
+})();