Motivation for this change

libxml2 1.9.7 supports the XML_CATALOG_FILES environment variable natively by using empty catalogfile argument.

The change does not have any effect on the package – directory trees are identical, up to self-referring hashes. Apparently, the various packages have a copy of the m4 files in their source trees so we will need to patch them too when we want to enable building docs for them.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.