Fix quite sprious compile error on VS2015 Preview.

VS2015 treats unary-ctor call as a variable declaration when
member name and any other class name are same, see following.

    struct foo
    {
        foo(int) {}
        void set() {}
    };

    struct set;

    int main()
    {
        int i;
        foo(i).set(); // VS2015 try to decl `i` here and conflict with above.
    }