Compilation fix for PCH-less build.

This should fix compilation without PCH after r75785.

See #2609.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75794 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/imaglist.cpp

@@ -24,6 +24,7 @@
 #endif
 
 #ifndef WX_PRECOMP
+    #include "wx/app.h"
     #include "wx/msw/wrapcctl.h" // include <commctrl.h> "properly"
     #include "wx/window.h"
     #include "wx/icon.h"