Fixed bug 2146 - Enable static linking of libSDL on Android

Denis Bernard

This patch to Android.mk adds support for static linking of libSDL for Android applications. A patched readme with static build instructions is also provided.

It does not break existing build environments setup according to the README-android.txt since the static library version will not be built in not required.

The static build uses the Android NDK module system (see docs/IMPORT-MODULE.html in the NDK folder and step 5 in the instructions below).

Instructions:
1. Copy the android-project directory wherever you want to keep your projects
   and rename it to the name of your project.
2. Create a symlink to SDL/src/main/android/SDL_android_main.c as
   <project>/jni/src/SDL_android_main.c
3. Rename <project>/jni/src/Android_static.mk to <project>/jni/src/Android.mk
   (overwrite the existing one)
4. Edit <project>/jni/src/Android.mk to include your source files
5. create and export an environment variable named NDK_MODULE_PATH that points
   to the parent directory of this SDL directory. e.g.:

   export NDK_MODULE_PATH="$PWD"/..

6. Edit <project>/src/org/libsdl/app/SDLActivity.java and remove the call to
   System.loadLibrary("SDL2") line 42.
7. Run 'ndk-build' (a script provided by the NDK). This compiles the C source

Although this requires an environment variable to be setup, it can be added once and for all to the main Android.mk of the project.

android-project/jni/src/Android_static.mk

@@ -0,0 +1,12 @@
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := main
+
+LOCAL_SRC_FILES := YourSourceHere.c
+
+LOCAL_STATIC_LIBRARIES := SDL2_static
+
+include $(BUILD_SHARED_LIBRARY)
+$(call import-module,SDL)LOCAL_PATH := $(call my-dir)