Update Android port

Update Android port

* INSTALL.android: Describe that apksigner is also required.
* configure.ac: Correctly add cross/Makefile to
SUBDIR_MAKEFILES.
* cross/Makefile.in: (config.status): Depend on
$(top_srcdir)/config.status.
* doc/emacs/input.texi (On-Screen Keyboards): Document how to
quit without a physical keyboard.
* java/org/gnu/emacs/EmacsNative.java (EmacsNative): New
function `quit'.
* java/org/gnu/emacs/EmacsWindow.java (EmacsWindow): New field
`lastVolumeButtonPress'.
(onKeyDown): Quit if necessary.
* m4/ndk-build.m4 (ndk_where_cc): Fix search if CC is not a
single word.
* src/android.c (android_open): Remove unused variable.
(quit): New function.
* src/androidmenu.c (android_process_events_for_menu): Allow
quitting the menu.
* src/xterm.c (handle_one_xevent, x_term_init, syms_of_xterm):
Implement features described above, so they work on free
operating systems.
* src/xterm.h (struct x_display_info): New fields `quit_keysym',
`quit_keysym_time'.