add FindSDL2.cmake file to fix windows built error

cmake/modules/FindSDL2.cmake

@@ -0,0 +1,17 @@
+# Locate SDL2 library and include directories
+find_path(SDL2_INCLUDE_DIR NAME SDL.h HINTS ENV SDL2DIR PATH_SUFFIXES include/SDL2 include)
+
+find_library(SDL2_LIBRARY NAME SDL2 HINTS ENV SDL2DIR PATH_SUFFIXES lib lib/x64 lib/x86)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(SDL2 DEFAULT_MSG SDL2_LIBRARY SDL2_INCLUDE_DIR)
+
+if(SDL2_FOUND AND NOT TARGET SDL2::SDL2)
+    add_library(SDL2::SDL2 UNKNOWN IMPORTED)
+    set_target_properties(SDL2::SDL2 PROPERTIES
+        IMPORTED_LOCATION "${SDL2_LIBRARY}"
+        INTERFACE_INCLUDE_DIRECTORIES "${SDL2_INCLUDE_DIR}")
+endif()
+
+mark_as_advanced(SDL2_INCLUDE_DIR SDL2_LIBRARY)
+