... so that all of 'exit', '_exit', '_Exit' work. 'exit' thus becomes the
standard 'newlib/libc/stdlib/exit.c'. (Getting 'atexit' functional needs
further work elsewhere.)
See also commit 5841b2f6a4208682264d03e3edfa0a09881932a6
"nvptx: Implement '_exit' instead of 'exit'".
