chiark-utils FTBFS against nettle 4.0 with:
summer.c:44:10: fatal error: nettle/md5-compat.h: No such file or directory
   44 | #include "nettle/md5-compat.h"
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.


nettle 4.0 is available in experimental (nettle4-dev). This is a API
breaking release, see the NEWS file.

  * Deleted md5-compat.h, and everything declared therein. Use
    the interface in md5.h instead (or even better, stop using md5).

cu Andreas