Remove PATH-tweaking in cygwin_create_process_env

Assume instead that the user will have configured PATH correctly,
knowing that if opam has added Cygwin's bin to PATH, it will have put it
in the correct place.

master_changes.md

@@ -78,6 +78,7 @@ users)
   * Fix incorrect deduplication of environment variables on update. Effect was that FOO += "" would occlude the value of FOO in the environment [#5837 @dra27]
   * Fix regression from #5356 on the detection of out-of-date environment variables. As part of a refactoring, a filter predicate got inverted [#5837 @dra27]
   * Unixify Windows paths in init shells scripts (sh, bash, zsh, fish & tsh) [#5797 @rjbou]
+  * `OpamProcess.cygwin_create_process_env` no longer adjusts PATH [#5832 @dra27]
   * Internal Cygwin installation's bin directory is placed as far down PATH as is necessary not to shadow `bash`, `tar`, `sort` or `git` [#5832 @dra27]
 
 ## Opamfile

src/core/opamProcess.ml

@@ -179,29 +179,6 @@ let cygwin_create_process_env prog args env fd1 fd2 fd3 =
           None
         end else
           Some (key ^ "=" ^ String.concat " " settings)
-    | "path" ->
-        let path_dirs = OpamStd.Sys.split_path_variable value in
-        let winsys = Filename.concat (OpamStd.Sys.system ()) "." |> String.lowercase_ascii in
-        let rec f prefix suffix = function
-        | dir::dirs ->
-            let contains_cygpath = Sys.file_exists (Filename.concat dir "cygpath.exe") in
-            if suffix = [] then
-              if String.lowercase_ascii (Filename.concat dir ".") = winsys then
-                f prefix [dir] dirs
-              else
-                if contains_cygpath then
-                  path_dirs
-                else
-                  f (dir::prefix) [] dirs
-            else
-              if contains_cygpath then begin
-                log ~level:2 "Moving %s to after %s in PATH" dir (List.hd prefix);
-                List.rev_append prefix (dir::(List.rev_append suffix dirs))
-              end else
-                f prefix (dir::suffix) dirs
-        | [] -> []
-        in
-        Some (key ^ "=" ^ String.concat ";" (f [] [] path_dirs))
     | _ ->
         Some item in
   let env = OpamStd.List.filter_map f env in