Compiling amanda with std=C23

Folks,

     Jason Tibbitts' comment about amanda not compiling with std=c23 got 
me a bit worried about losing amanda as part of Fedora, so I thought I'd 
give a try at tweaking the code. The result is pushed to GitHub as
   https://www.github.com/louhafer/amanda
This not a fork, it's an independent repo. Tried a fork, that just 
seemed messy beyond redemption.

     The code blocking compilation was all in ndmp-src. I went a bit 
further and tried to update some of the outdated GLib usage and pick off 
a few more function signature mismatches.

     This is targeted to Fedora --- starting point is the zmanda/amanda 
community-3.5.4 tag, with a bunch of patches from the Fedora source rpm.

     I have no way of testing whether the changes are correct. My simple 
use case is backing up a few home systems to disk with ssh. `Works for 
me', as the saying goes. But the various tweaks may be useful to others.

               Lou