ISO C 23 ahead

[Bruno Haible]

The final draft of ISO C 23 is available:
  https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3047.pdf
and the editor was so nice to summarize what's in it:
  https://thephd.dev/c23-is-coming-here-is-what-is-on-the-menu

For Gnulib, the most interesting additions are:
  - <stdbit.h>
  - <stdckdint.h>
  - memset_explicit.
But there's more; see the Annex M.1 for details.

Bruno