_Exit detection

[Thien-Thi Nguyen]

GNU RCS uses gnulib module ‘stdlib’, which AFAICT does not
detect missing ‘_Exit’, e.g., when using dietlibc:

https://savannah.gnu.org/bugs/?30372

I am unsure where/how to fix this and would be grateful for any tips.
Specifically:

- Is this something gnulib can/should handle?
- If not, what is the best (gnulib-compatible)
  way to detect missing ‘_Exit’?
- Moving laterally, is it poor style to use ‘_Exit’
  (as opposed to plain old ‘_exit’) in the first place?

I look forward to learning from your repsonses.

thi