On sid, llvm-toolchain-5.0 has libctypes-ocaml-dev as a build dependency.
# apt install libctypes-ocaml-dev
...
The following packages have unmet dependencies:
libctypes-ocaml-dev : Depends: libctypes-ocaml-v0kb0
Depends: ocaml-nox-4.02.3 but it is not installable
E: Unable to correct problems, you have held broken packages.
Sid has ocaml-nox has only a fresher version:
# apt-cache policy ocaml-nox
ocaml-nox:
Installed: 4.05.0-9
Candidate: 4.05.0-9
Version table:
*** 4.05.0-9 500
100 /var/lib/dpkg/status
This means that llvm-toolchain-5.0 cannot be built on sid.
--
Jean-Christophe Manciot