CMake: Only find and link to SDL when needed

src/qt/CMakeLists.txt

@@ -284,6 +284,15 @@ if(WIN32 AND NOT SDL_JOYSTICK)
     target_sources(plat PRIVATE win_joystick_rawinput.c)
     target_link_libraries(86Box hid)
 else()
+    find_package(SDL2 REQUIRED)
+    include_directories(${SDL2_INCLUDE_DIRS})
+    if(STATIC_BUILD AND TARGET SDL2::SDL2-static)
+        target_link_libraries(86Box SDL2::SDL2-static)
+    elseif(TARGET SDL2::SDL2)
+        target_link_libraries(86Box SDL2::SDL2)
+    else()
+        target_link_libraries(86Box ${SDL2_LIBRARIES})
+    endif()
     target_sources(plat PRIVATE sdl_joystick.c)
 endif()