Testcase fails to work with gcc, works with clang.

=====
struct QSize
{
    QSize(int w, int h) : wd(w), ht(h) {}

    QSize expandedTo() const __attribute__ ((__warn_unused_result__))
    {
        return QSize(2, 3);
    }

private:
    int wd;
    int ht;
};

void foo()
{
    QSize sz(2, 2);
    sz.expandedTo();
}
=====
$ g++ testcase.cpp -c -Wunused-result

$ clang++ testcase.cpp -c -Wunused-result
testcase.cpp:18:5: warning: ignoring return value of function declared with warn_unused_result attribute [-Wunused-result]
    sz.expandedTo();
    ^~~~~~~~~~~~~
1 warning generated.