xcb: don't allow isAtLeastXI2{1,2} in builds without Xinput2

.. thus making it purely into a _runtime_ check of XInput 2 version.

If Qt was build with -no-xinput2, it does not make sense to compile
in code that always returns "false". Simply exclude code that is not
relevant for -no-xinput2 builds with XCB_USE_XINPUT2 ifdefs. In
addition, this improves readability of the code.

Now, trying to use ::isAtLeastXI21() in a -no-xinput2 build will
result in the following build error:

error: ‘class QXcbConnection’ has no member named ‘isAtLeastXI21’

Change-Id: If242510d43d71829b327edc1f76322f3a0db0e08
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/plugins/platforms/xcb/qxcbconnection.h

@@ -428,16 +428,8 @@ public:
 
 #if QT_CONFIG(xinput2)
     void xi2Select(xcb_window_t window);
-#endif
-#ifdef XCB_USE_XINPUT21
     bool isAtLeastXI21() const { return m_xi2Enabled && m_xi2Minor >= 1; }
-#else
-    bool isAtLeastXI21() const { return false; }
-#endif
-#ifdef XCB_USE_XINPUT22
     bool isAtLeastXI22() const { return m_xi2Enabled && m_xi2Minor >= 2; }
-#else
-    bool isAtLeastXI22() const { return false; }
 #endif
 
     void sync();

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -2185,7 +2185,9 @@ void QXcbWindow::handleButtonPressEvent(int event_x, int event_y, int root_x, in
     QPoint global(root_x, root_y);
 
     if (isWheel) {
+#if QT_CONFIG(xinput2)
         if (!connection()->isAtLeastXI21()) {
+#endif
             QPoint angleDelta;
             if (detail == 4)
                 angleDelta.setY(120);
@@ -2198,7 +2200,9 @@ void QXcbWindow::handleButtonPressEvent(int event_x, int event_y, int root_x, in
             if (modifiers & Qt::AltModifier)
                 std::swap(angleDelta.rx(), angleDelta.ry());
             QWindowSystemInterface::handleWheelEvent(window(), timestamp, local, global, QPoint(), angleDelta, modifiers);
+#if QT_CONFIG(xinput2)
         }
+#endif
         return;
     }