Both the debug and release jobs would upload artifacts, with the same name, which ghactions of course accepted without question. Snapshot 240 happens to have been released correctly (so all binaries are release builds), but that's just luck. I'd thought I'd fixed this problem with another commit, but turns out I hadn't.
Also factor out a bunch of variables so I won't mess up in the future.
Also restructure meson.build and the ghactions workflow a bit, and enable -ffunction-sections and -fdata-sections.
Note that starcatcher uploads have not been tested and most likely don't work.
