[JS IR BE] Support integer operation overflow

libraries/stdlib/js/irRuntime/misc.kt

@@ -0,0 +1,10 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.js
+
+// TODO: Polyfill
+fun imul(a: dynamic, b: dynamic) =
+    js("((a & 0xffff0000) * (b & 0xffff) + (a & 0xffff) * (b | 0)) | 0")