In reply to @solitudesf "x11 is forgotten...": The SDL backend will work fine
on X11, and the Vulkan backend is the most complex (most LoC at least) so easier
to port the GL backend for example. The SDL backend is mainly for input, there
is a separate SDL renderer backend too. ImGUI just needs platform backend and
render backend for whatever platform, and they are mostly glue code,

I have the C++ source for ImGUI itself and the C wrapper just building as-is
with `{.compile.}` and then Futhark-built wrappers for Vulkan, SDL and the C
ImGUI API.