Install fails with opam due to Unbound module Big_int

[dbrumley]

Build fails due to Big_int being unbound.

$ opam switch 
#  switch   compiler             description
→  4.12.0   ocaml-system.4.12.0  4.12.0
   default  ocaml.4.12.0         default

$ opam install orm          
The following actions will be performed:
  ∗ install orm 0.7.1

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><>  🐫 
⬇ retrieved orm.0.7.1  (cached)
[ERROR] The compilation of orm.0.7.1 failed at "make".

#=== ERROR while compiling orm.0.7.1 ==========================================#
# context     2.1.0 | macos/x86_64 | ocaml-system.4.12.0 | https://opam.ocaml.org#7247859e
# path        ~/.opam/4.12.0/.opam-switch/build/orm.0.7.1
# command     ~/.opam/opam-init/hooks/sandbox.sh build make
# exit-code   2
# env-file    ~/.opam/log/orm-95495-692be4.env
# output-file ~/.opam/log/orm-95495-692be4.out
### output ###
# [...]
# Use Array.make/ArrayLabels.make instead.
# File "_none_", line 1:
# Warning 58 [no-cmx-file]: no cmx file was found in path for module Dyntype, and its interface was not compiled with -opaque
# ocamlfind ocamlopt -package sqlite3,dyntype.syntax -c -annot -for-pack Orm sql_get.ml
# File "sql_get.ml", line 76, characters 53-78:
# 76 | 		| `Big_int i -> int_like name (fun i -> Data.TEXT (Big_int.string_of_big_int i)) i
#                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: Unbound module Big_int
# make[3]: *** [sql_get.cmi] Error 2
# make[2]: *** [native-code-library] Error 2
# make[1]: *** [all] Error 2
# make: *** [all] Error 2



<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><>  🐫 
┌─ The following actions failed
│ λ build orm 0.7.1
└─ 
╶─ No changes have been performed