Backends: SDL: fix build on WinRT (#6019, #5974) - version for docking branch

Amend da83253

backends/imgui_impl_sdl.cpp

@@ -418,7 +418,7 @@ static bool ImGui_ImplSDL2_Init(SDL_Window* window, SDL_Renderer* renderer, void
     SDL_VERSION(&info.version);
     if (SDL_GetWindowWMInfo(window, &info))
     {
-#ifdef _WIN32
+#if defined(SDL_VIDEO_DRIVER_WINDOWS)
         main_viewport->PlatformHandleRaw = (void*)info.info.win.window;
 #elif defined(__APPLE__) && defined(SDL_VIDEO_DRIVER_COCOA)
         main_viewport->PlatformHandleRaw = (void*)info.info.cocoa.window;
@@ -777,7 +777,7 @@ static void ImGui_ImplSDL2_CreateWindow(ImGuiViewport* viewport)
     SDL_VERSION(&info.version);
     if (SDL_GetWindowWMInfo(vd->Window, &info))
     {
-#if defined(_WIN32)
+#if defined(SDL_VIDEO_DRIVER_WINDOWS)
         viewport->PlatformHandleRaw = info.info.win.window;
 #elif defined(__APPLE__) && defined(SDL_VIDEO_DRIVER_COCOA)
         viewport->PlatformHandleRaw = (void*)info.info.cocoa.window;