make a MCE(Minimal Complete Example) for gcc 13.2.0 bug in QTransform

On Ubuntu 24.04

gcc version 13.2.0 (Ubuntu 13.2.0-23ubuntu4) seems to remove some
code in release builds that is embedded in a macro in qtransfrom.cpp.
This patch changes the macro into a function such that it is not
removed by gcc.

It seems like the switch statement is (wrongly) optimized away if it is
embedded in the QTransform::map(QPolygonF) overload. nx and ny are
always 0 (as initialized by QPolygonF) after the macro (but only within
the QTransform::map(QPolygonF) function.

The bug happens only in a release build. Added debug messages of nx and
ny created no output, adding qDebug() << t, which made the macro work.

It seems that a complex combination of macro and switch statement can
tigger the bug in gcc. So rewriting the macro as a function works around
the bug.

More details in https://bugreports.qt.io/browse/QTBUG-127723 and https://codereview.qt-project.org/c/qt/qtbase/+/581308

We'd better to have a MCE and submit to gcc upstream.