bug#24674: Dropbear bundled libraries

[Leo Famulari <leo@famulari.name>]

On Fri, Dec 18, 2020 at 08:53:23PM +0100, zimoun wrote:
> with the last update 2020-10-29, I propose to mark it as ’severe’ and
> put it in the list of bugs which should be fixed for the next (or
> next-next) release.  WDYT?

Dropbear 2020.79 includes this text in the CHANGES file:

------
- Upgrade libtomcrypt to 1.18.2 and libtommath to 1.2.0, many thanks to Steffen Jaeckel for
  updating Dropbear to use the current API. Dropbear's configure script will check 
  for sufficient system library versions, otherwise using the bundled versions.
------

And in 2020.80:

------
- Improve checking libtomcrypt version compatibility
------

So, it might be possible now to use "system" copies of these libraries.
Previously, I couldn't figure out how to do it work or if Dropbear would
continue to work correctly.

We have a package of libtommath 1.2.0.

TODO:
1) Package libtomcrypt 1.18.2
2) Try building Dropbear with libtommath and libtomcrypt Guix packages