Just to be perfectly clear, ... you do
not want to build a recent version of Sigil from source on Ubuntu, but instead build a really old version of Sigil circa version 0.9.9, which uses the now defunct QtWebKit. And you want to do this on a Raspberry Pi?
Is that correct?
If so, I very much doubt that at all doable or even possible as I am not sure the old QtWebKit source code is still around and even if so if it is buildable on a Raspberry Pi.
You do know about newer Sigil's External XEditor Preferences and Sigil's companion program PageEdit, right? PageEdit is easily launched from within Sigil and does much of the wysiwyg editing that the older BookView enabled. Check out the screen shots at:
https://github.com/Sigil-Ebook/PageEdit and you will see how close to the old BookView it truly is.
You would stand a much higher chance of building current Sigil and PageEdit from source on a recent Ubuntu version.
Either way good luck with that.