cmake: set SYSTEM property in SDL3Config.cmake for compatibility with older CMake versions

CMakeLists.txt

@@ -3212,9 +3212,6 @@ endif()
 add_library(SDL3_Headers INTERFACE)
 add_library(SDL3::Headers ALIAS SDL3_Headers)
 set_property(TARGET SDL3_Headers PROPERTY EXPORT_NAME "Headers")
-if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.25")
-  set_property(TARGET SDL3_Headers PROPERTY EXPORT_NO_SYSTEM "TRUE")
-endif()
 target_include_directories(SDL3_Headers
   INTERFACE
     "$<BUILD_INTERFACE:${SDL3_BINARY_DIR}/include>"

cmake/SDL3Config.cmake.in

@@ -14,6 +14,9 @@ set(_sdl3_framework @SDL_FRAMEWORK@)
 # Find SDL3::Headers
 if(NOT TARGET SDL3::Headers)
   include("${CMAKE_CURRENT_LIST_DIR}/SDL3headersTargets.cmake")
+  if(NOT CMAKE_VERSION VERSION_LESS "3.25")
+    set_property(TARGET SDL3::Headers PROPERTY SYSTEM 0)
+  endif()
 endif()
 set(SDL3_Headers_FOUND TRUE)