Fixed Android error on static lib build, if relative NDK_MODULE_PATH used

Stefan Pöschel

if the variable NDK_MODULE_PATH is set to a relative path (like "../"),
compiling of a static SDL lib fails with an error similar to this:
make: *** No rule to make target
`..//android_libs/SDL/..//android_libs/SDL/src/main/android/SDL_android_main.c',
needed by
`obj/local/armeabi/objs/SDL2_static/__//android_libs/SDL/src/main/android/SDL_android_main.o'.
 Stop.

Regarding the shared lib, this is already prevented by a "subst" command
in the /Android.mk, which removes all occurences of "$(LOCAL_PATH)/".
The attached patch does the same with the additional
"SDL_android_main.c", which is included for build the static SDL lib.
Add controller mapping for Bluetooth DualShock 4 controllers on Linux

Frank Praznik

Add a gamepad mapping entry for Bluetooth DualShock 4 controllers on Linux.
The button mapping is the same as the USB controller, but the GUID is
different.