It kept complaining about that until I realised there should be an external crate for it.
warn:
warn: New solution is incomplete.
warn: +π¦ gnat 12.2.1 (new,gnat_native,indirect,binary)
warn: + gnatcoll 23.0.0 (new,indirect)
warn: + gnatcoll_gmp 23.0.0 (new,indirect)
warn: + gnatcoll_iconv 23.0.0 (new,indirect)
warn: + gpr_unit_provider 23.0.0 (new)
warn: + langkit_support 23.0.0 (new,indirect)
warn: + libadalang 23.0.0 (new)
warn: +π libgmp * (new,external,indirect)
warn: + libgpr 23.0.0 (new,indirect)
warn: + libgpr2 23.0.0 (new)
warn: + markdown 23.0.0 (new)
warn: + vss 23.0.0 (new)
warn: + xmlada 23.0.0 (new,indirect)
It does build, but it does also complain.