ocamlPackages.carton: Tests require getconf

https://github.com/mirage/ocaml-git/blob/471406dde6c3056ea49547de379fef12871da48b/bin/fiber/fiber.ml#L132

pkgs/development/ocaml-modules/carton/carton-find-getconf.patch

@@ -0,0 +1,13 @@
+diff --git a/bin/fiber/fiber.ml b/bin/fiber/fiber.ml
+index 188a92cc9..6087a8687 100644
+--- a/bin/fiber/fiber.ml
++++ b/bin/fiber/fiber.ml
+@@ -129,7 +129,7 @@ let worker pool =
+ 
+ let get_concurrency () =
+   try
+-    let ic = Unix.open_process_in "getconf _NPROCESSORS_ONLN" in
++    let ic = Unix.open_process_in "@getconf@/bin/getconf _NPROCESSORS_ONLN" in
+     let close () = ignore (Unix.close_process_in ic) in
+     let sc = Scanf.Scanning.from_channel ic in
+     try

pkgs/development/ocaml-modules/carton/default.nix

@@ -3,6 +3,7 @@
 , checkseum, logs, psq, fmt
 , result, rresult, fpath, base64, bos, digestif, alcotest
 , crowbar, alcotest-lwt, lwt, findlib, mirage-flow, cmdliner, hxd
+, getconf, substituteAll
 }:
 
 buildDunePackage rec {
@@ -16,6 +17,13 @@ buildDunePackage rec {
     sha256 = "sha256-7mgCgu87Cn4XhjEhonlz9lhgTw0Cu5hnxNJ1wXr+Qhw=";
   };
 
+  patches = [
+    (substituteAll {
+      src = ./carton-find-getconf.patch;
+      getconf = "${getconf}";
+    })
+  ];
+
   # remove changelogs for mimic and the git* packages
   postPatch = ''
     rm CHANGES.md