Lite exit support.
* README: Add information about lite-exit.
* acconfig.h (_LITE_EXIT): New macro.
* configure.in (enable-lite-exit): New option.
(_LITE_EXIT): Define new macro.
* configure: Regenerated.
* newlib.hin (_LITE_EXIT): New macro.
* libc/stdlib/__atexit.c [_LITE_EXIT]: Add dummy explicit
reference to __call_exitprocs.
* libc/stdlib/cxa_atexit.c [_LITE_EXIT]: Make __register_exitproc a
weak reference.
* libc/stdlib/exit.c (exit)[_LITE_EXIT]: Remove TWS and weakly reference
__call_exitprocs.