[DiapDealer]

If you built Sigil and it works, then you built sogil-gumbo. It's integral and Sigil will not build or function at all without it. The only two pieces you would even have a say in whether or not you could build/use Sigil without them is css-parser and dulwich. Both provide functionality that would be missing from Sigil without them. The Arch package (which has already been updated to 1.5.1) includes all of the things you mentioned as required dependencies.

To be perfectly clear: only two of the items you mentioned are actually external modules (css-parser and dulwich are both python modules that Sigil requires for functionality). Everything else is integral C/C++ source code included with Sigil.