ocaml-freestanding 0.6.4

Error log

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

Opam plugin "depext" may require upgrading/reinstalling. Reinstall the plugin on the current switch? [Y/n] y
The following actions will be performed:
  - recompile opam-depext 1.2.3

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-> retrieved opam-depext.1.2.3  (cached)
-> removed   opam-depext.1.2.3
-> installed opam-depext.1.2.3
Done.

<><> opam-depext.1.2.3 installed successfully <><><><><><><><><><><><><><><><><>
=> opam-depext is unnecessary when used with opam >= 2.1. Please use opam install directly instead
# Run eval $(opam env) to update the current shell environment

<><> Carrying on to "opam depext -viy ocaml-freestanding.0.6.4" <><><><><><><><>

Since version 2.1, opam now handles external dependencies alongside OCaml ones, and the `depext` plugin interface is provided for backwards compatibility only. Consider using your usual `opam install` command to install both OCaml and system dependencies, or `opam install <pkg> --depext-only` if you want to only install external dependencies.
# Detecting depexts using vars: arch=x86_64, os=linux, os-distribution=debian, os-family=debian
[ERROR] No solution for ocaml-freestanding.0.6.4:   * Incompatible packages:
            - (invariant) -> ocaml-base-compiler = 5.1.1
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> dkml-base-compiler
            You can temporarily relax the switch invariant with `--update-invariant'
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler < 3.07+1 | ocaml-system < 3.07+1 | ocaml-variants < 3.8~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions: 'sys-ocaml-version = "3.07"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.07+1 | ocaml-system = 3.07+1 | ocaml-variants < 3.8~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions: 'sys-ocaml-version = "3.07+1"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.07+2 | ocaml-system = 3.07+2 | ocaml-variants < 3.8~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions: 'sys-ocaml-version = "3.07+2"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.08.0 | ocaml-system < 3.08.1~ | ocaml-variants < 3.08.1~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.0"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.08.1 | ocaml-system < 3.08.2~ | ocaml-variants < 3.08.2~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.1"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.08.2 | ocaml-system < 3.08.3~ | ocaml-variants < 3.08.3~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.2"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.08.3 | ocaml-system < 3.08.4~ | ocaml-variants < 3.08.4~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.3"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.08.4 | ocaml-system < 3.08.5~ | ocaml-variants < 3.08.5~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.4"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-base-compiler = 3.09.0 | ocaml-system < 3.09.1~ | ocaml-variants < 3.09.1~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.09.0"'
            no matching version
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-variants -> ocaml-beta
            unmet availability conditions: 'enable-ocaml-beta-repository'
          * Missing dependency:
            - ocaml-freestanding = 0.6.4 -> ocaml < 4.13.0 -> ocaml-variants -> system-msvc
            unmet availability conditions: 'os = "win32"'


Command failed: opam --cli=2.1 list --readonly --external '--resolve=ocaml-freestanding.0.6.4' --color=never returned 20