This hardens against an observed regression where dependency files were
being dumped into the build root. The dependency-chain for
move-animation scripts is still broken, however, as there is a race
condition on which dependency-file is ingested by Ninja, which then gets
applied to all output files since they share a common name. Meson
appears to not respect "preserve_path_from" when generating the path for
the depfile, so this was always broken for those scripts.
