mingw compilation for singleapp

singleapplication/Windows.md

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+Windows Specific Implementations
+================================
+
+Setting the foreground window
+-----------------------------
+
+In the `instanceStarted()` example in the `README` we demonstrated how an
+application can bring it's primary instance window whenever a second copy
+of the application is started.
+
+On Windows the ability to bring the application windows to the foreground is
+restricted, see [`AllowSetForegroundWindow()`][AllowSetForegroundWindow] for more
+details.
+
+The background process (the primary instance) can bring its windows to the
+foreground if it is allowed by the current foreground process (the secondary
+instance). To bypass this `SingleApplication` must be initialized with the
+`allowSecondary` parameter set to `true` and the `options` parameter must
+include `Mode::SecondaryNotification`, See `SingleApplication::Mode` for more
+details.
+
+Here is an example:
+
+```cpp
+if( app.isSecondary() ) {
+    // This API requires LIBS += User32.lib to be added to the project
+    AllowSetForegroundWindow( DWORD( app.primaryPid() ) );
+}
+
+if( app.isPrimary() ) {
+    QObject::connect(
+        &app,
+        &SingleApplication::instanceStarted,
+        this,
+        &App::instanceStarted
+    );
+}
+```
+
+```cpp
+void App::instanceStarted() {
+    QApplication::setActiveWindow( [window/widget to set to the foreground] );
+}
+```
+
+[AllowSetForegroundWindow]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms632668.aspx