If ac_x_libraries is empty it means that the library's found in the default path,
so we skip adding it to the XLIB variable as it screws up the search path.
If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.
Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.
Sam Lantinga
Gabriel Jacobo