change build system to CMake and use SDL3 for everything

libs/SDL3/android-project/app/jni/CMakeLists.txt

@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.6)
+
+project(GAME)
+
+# SDL sources are in a subfolder named "SDL"
+add_subdirectory(SDL)
+
+# Compilation of companion libraries
+#add_subdirectory(SDL_image)
+#add_subdirectory(SDL_mixer)
+#add_subdirectory(SDL_ttf)
+
+# Your game and its CMakeLists.txt are in a subfolder named "src"
+add_subdirectory(src)
+