Usually the function name is dropped if the function is a function expression. But when `ie8` option is enabled, the function name is kept and mangled which may break legacy Safari for said reason. Since symbol names are now [mangled from within](https://github.com/mishoo/UglifyJS2/pull/2948#issuecomment-368095376), this fix adds argument names to existing names when mangling the name of a function expression.
