Let's stop using BuildSourcesEphemeral= and instead make sure we don't
generate any auxiliary files during the mkosi build process.
We achieve this through a combination of trap to remove any new files
we create and bind mounts from /tmp over existing files whenever we need
to modify an existing file.
We also add a CI step to ensure we don't regress
- Add missing '--' delimiter
- Use the new BuildSubdirectory JSON field to figure out the build
subdirectory.
- Remove the /usr/include path mapping for now. This means we can't
jump into system headers anymore if they don't exist on the host,
we can find a way to add this back later if it turns out to be
crucial.
If the editor that invokes mkosi.clangd is a flatpak, let's make sure
that mkosi is run on the host and not in the flatpak sandbox since it
won't be installed there.
We're just running a language server so no need to put a writable
overlay on top of the build sources to prevent modifications. This
hopefully helps the language server track modifications to the source
files better.
