xmlrpc_c: 1.33.17 -> 1.39.12

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- ran `/nix/store/4cdb0kvm05d8390pg3agfy7hjm9ygd9s-xmlrpc-c-1.39.12/bin/xmlrpc-c-config --help` got 0 exit code
- ran `/nix/store/4cdb0kvm05d8390pg3agfy7hjm9ygd9s-xmlrpc-c-1.39.12/bin/xmlrpc-c-config --version` and found version 1.39.12
- ran `/nix/store/4cdb0kvm05d8390pg3agfy7hjm9ygd9s-xmlrpc-c-1.39.12/bin/xmlrpc-c-config --help` and found version 1.39.12
- found 1.39.12 with grep in /nix/store/4cdb0kvm05d8390pg3agfy7hjm9ygd9s-xmlrpc-c-1.39.12
- directory tree listing: https://gist.github.com/02ef530309005ffeedbc4af16ffd467c