Bug 1815964: Remove MinGW ifdefs in Virtual Desktop Manager r=firefox-build-system-reviewers,ahochheiden

It's not clear to me why we define IVirtualDesktopManager when it's
available in headers.  I do know that because we are defining it instead
of getting it from headers, we aren't defining the UUID of it in the
MinGW way (which of course is done in the MinGW headers) so if we
want to continue doing that, we will need to add that.  Although
it would be better if we could remove it entirely and use the headers...

Differential Revision: https://phabricator.services.mozilla.com/D169376

widget/windows/nsWindow.cpp

@@ -594,7 +594,6 @@ class InitializeVirtualDesktopManagerTask : public Task {
 #endif
 
   virtual bool Run() override {
-#ifndef __MINGW32__
     if (!IsWin10OrLater()) {
       return true;
     }
@@ -608,7 +607,6 @@ class InitializeVirtualDesktopManagerTask : public Task {
     }
 
     gVirtualDesktopManager = desktopManager;
-#endif
     return true;
   }
 };

widget/windows/nsWindow.h

@@ -97,6 +97,11 @@ IVirtualDesktopManager : public IUnknown {
       __RPC__in HWND topLevelWindow, __RPC__in REFGUID desktopId) = 0;
 };
 
+#ifdef __MINGW32__
+__CRT_UUID_DECL(IVirtualDesktopManager, 0xa5cd92ff, 0x29be, 0x454c, 0x8d, 0x04,
+                0xd8, 0x28, 0x79, 0xfb, 0x3f, 0x1b)
+#endif
+
 /**
  * Native WIN32 window wrapper.
  */