ocaml-src 4.12.1

Error log

The package failed to build. The error log from opam follows.

[ERROR] Package conflict!
  * Incompatible packages:
    - (invariant) -> ocaml-base-compiler = 5.1.1
    - ocaml-src = 4.12.1 -> ocaml = 4.12.1 -> dkml-base-compiler
    You can temporarily relax the switch invariant with `--update-invariant'
  * Incompatible packages:
    - (invariant) -> ocaml-base-compiler = 5.1.1
    - ocaml-src = 4.12.1 -> ocaml = 4.12.1 -> ocaml-variants >= 4.12.1~
  * Missing dependency:
    - ocaml-src = 4.12.1 -> ocaml = 4.12.1 -> ocaml-variants >= 4.12.1~ -> system-msvc
    unmet availability conditions: 'os = "win32"'

No solution found, exiting