Everything about meson

I was a bit anxious about running our poppler meson build in CI, because it's the real test, you know? "Works on my machine" only goes so far, things have a tendency to break once you try to make them reproducible.

It took a hot minute.

Well, yeah. I got to contribute to a bunch of open-source projects in the meantime though, so I'm fairly pleased with it!

• libffi (for static linking)
• cairo (more static linking!)
• proxy-libintl (more static linking!)
• expat (static linking strikes again)
• poppler (for file descriptor stuff not properly gated on Windows, closed in favor of a similar MR)
• glib (work in progress, involves thread-local storage and dynamic linker/loader cursedness)