ocaml-migrate-parsetree fails to build on 4.14.0+trunk

[shubhamkumar13]

This is an error log from sandmark where I am trying to build ocaml-migrate-parsetree.2.1.0 with 4.14.0+trunk and dune.2.9.0

#=== ERROR while compiling ocaml-migrate-parsetree.2.1.0+stock ================#
# context              2.0.6 | linux/x86_64 | ocaml-base-compiler.4.14.0+trunk | file:///home/shubham/sandmark/dependencies
# path                 ~/sandmark/_opam/4.14.0+trunk/.opam-switch/build/ocaml-migrate-parsetree.2.1.0+stock
# command              ~/sandmark/_opam/4.14.0+trunk/bin/dune build -p ocaml-migrate-parsetree -j 27
# exit-code            1
# env-file             ~/sandmark/_opam/log/ocaml-migrate-parsetree-14664-9055a8.env
# output-file          ~/sandmark/_opam/log/ocaml-migrate-parsetree-14664-9055a8.out
### output ###
#        ocaml src/ast-version (exit 1)
# (cd _build/default/src && /home/shubham/sandmark/_opam/4.14.0+trunk/bin/ocaml config/gen.ml 4.14.0+dev0-2021-06-03)
# Unknown OCaml version 4.14.0+dev0-2021-06-03