The [documentation](https://source.winehq.org/WineAPI/AtlAxWinInit.html) for `AtlAxWinInit` states that it initialises ATL's control hosting code by registering window classes "_and some messages_". MSDN's documentation phrases this as "_plus a couple of custom window messages_", but Wine's implementation didn't register any custom window messages. Logging calls to `RegisterWindowMessage` showed that Visual Studio 2005, when going into Options -\> Projects and Solutions -\> VC++ Directories, calls this function to get the message IDs for custom messages name `WM_ATLGETCONTROL` and `WM_ATLGETHOST`. I've then registered those same messages in `AtlAxWinInit` and logged when they were called in `AtlAxWin_wndproc`. Since they were called with 0 for both `wParam` and `lParam`, the only sensible implementation would be routing the calls through `AtlAxGetControl` and `AtlAxGetHost` and returning the `IUnknown` pointer from the window procedure. This minor change now makes the VC++ Directories control in Visual Studio 2005 work as expected (and probably other stuff too). In that, it fixes one of the problems listed on the [Visual Studio 2005 AppDb page](https://appdb.winehq.org/objectManager.php?sClass=version&iId=4494), specifically as described in the comment "Building" posted by Dave on 2021-08-01. -- v6: Added tests for proper handling of WM_ATLGETCONTROL and WM_ATLGETHOST. https://gitlab.winehq.org/wine/wine/-/merge_requests/10869