I was about to launch another “I don’t wanna be a hacker rant,” about the evils of the auto tools etc., when I realized I was just a doofus. If one actually reads the error messages pkg-config so helpfully offers, rather than rants….
So now gedit builds, on account of because gtk-sourceview builds, and i can get on with things.
(Updated moments later: I take it all back. It still won’t build. Consider this now ranted.)