File fix-assume-SDL2-target-is-always-available.patch of Package celestia

--- a/src/celestia/sdl/CMakeLists.txt
+++ b/src/celestia/sdl/CMakeLists.txt
@@ -70,11 +70,17 @@ target_link_libraries(celestia-sdl PRIVA
 
 set_target_properties(celestia-sdl PROPERTIES CXX_VISIBILITY_PRESET hidden)
 
-if(MINGW)
-  target_compile_definitions(celestia-sdl PRIVATE SDL_MAIN_HANDLED)
+if(TARGET SDL2::SDL2main AND TARGET SDL2::SDL2)
+  if(MINGW)
+    target_compile_definitions(celestia-sdl PRIVATE SDL_MAIN_HANDLED)
+  endif()
+  target_link_libraries(celestia-sdl PRIVATE SDL2::SDL2main SDL2::SDL2)
+  target_link_libraries(imgui PUBLIC SDL2::SDL2)
+else()
+  target_include_directories(celestia-sdl PRIVATE ${SDL2_INCLUDE_DIRS})
+  target_link_libraries(celestia-sdl PRIVATE ${SDL2_LIBRARIES})
+  target_link_libraries(imgui PUBLIC ${SDL2_LIBRARIES})
 endif()
-target_link_libraries(celestia-sdl PRIVATE SDL2::SDL2main SDL2::SDL2)
-target_link_libraries(imgui PUBLIC SDL2::SDL2)
 
 if(WIN32)
   install(