Rework Cygwin package list needed for opam and OCaml for Windows

mingw images also don't need msvs-tools.

Author: MisterDA

src-opam/opam.ml

@@ -431,22 +431,24 @@ let windows_mingw_opam2 ?win10_revision ?winget ?(labels = []) ?arch
     install_winget ?win10_revision ?winget version
   in
   let opams_image =
+    let packages =
+      (* dra27: we only need g++ in the "builder" image so that
+         opam-putenv gets built properly and so that opam is built
+         with the internal solver as well *)
+      "mingw64-x86_64-gcc-g++" :: "mingw64-i686-gcc-g++"
+      :: Windows.Cygwin.mingw_packages
+    in
     Windows.header ~alias:"opam-builder" ?win10_revision ~version ()
     @@ Windows.sanitize_reg_path ()
-    @@ Windows.Cygwin.(
-         install_cygwin
-           ~extra:
-             ("git" :: "patch" :: "mingw64-x86_64-gcc-g++"
-            :: "mingw64-i686-gcc-g++" :: mingw_packages)
-           ())
+    @@ Windows.Cygwin.install_cygwin ~extra:packages ()
     @@ install_opams_windows opam_master_hash opam_branches
   in
   (* 2022-10-12: Docker Engine 20.10.18 on Windows fails copying
      C:\cygwin64, so we cannot build Cygwin in a separate image. *)
   let ocaml_for_windows =
-    let extra = Windows.Cygwin.mingw_packages in
-    let extra, pkgs = Windows.Cygwin.ocaml_for_windows_packages ~extra () in
-    Windows.Cygwin.install_cygwin ~msvs_tools:true ~extra () @@ pkgs
+    let packages, setup = Windows.Cygwin.install_ocaml_for_windows () in
+    let packages = Windows.Cygwin.mingw_packages @ packages in
+    Windows.Cygwin.install_cygwin ~extra:packages () @@ setup
   in
   parser_directive (`Escape '`')
   @@ comment "Autogenerated by OCaml-Dockerfile scripts"
@@ -483,17 +485,18 @@ let windows_msvc_opam2 ?win10_revision ?winget ?(labels = []) ~opam_hashes
   (* 2022-10-12: Docker Engine 20.10.18 on Windows fails copying
      C:\cygwin64, so we cannot build Cygwin in a separate image. *)
   let ocaml_for_windows =
-    let extra, vs_build_tools =
+    let packages, vs_build_tools =
       ( Windows.Cygwin.msvc_packages,
         Windows.install_visual_studio_build_tools
           [
             "Microsoft.VisualStudio.Component.VC.Tools.x86.x64";
             "Microsoft.VisualStudio.Component.Windows10SDK.18362";
           ] )
     in
-    let extra, pkgs = Windows.Cygwin.ocaml_for_windows_packages ~extra () in
-    Windows.Cygwin.install_cygwin ~msvs_tools:true ~extra ()
-    @@ vs_build_tools @@ pkgs
+    let ofw_packages, ofw_setup = Windows.Cygwin.install_ocaml_for_windows () in
+    Windows.Cygwin.install_cygwin ~msvs_tools:true
+      ~extra:(packages @ ofw_packages) ()
+    @@ vs_build_tools @@ ofw_setup
   in
   parser_directive (`Escape '`')
   @@ comment "Autogenerated by OCaml-Dockerfile scripts"

src-opam/windows.ml

@@ -249,13 +249,24 @@ module Cygwin = struct
       "flexdll=" ^ flexdll_version;
     ]
 
-  let mingw_packages = [ "make"; "diffutils"; "mingw64-x86_64-gcc-core" ]
-  let msvc_packages = [ "make"; "diffutils" ]
+  let mingw_packages =
+    [ "make"; "diffutils"; "patch"; "mingw64-x86_64-gcc-core"; "git" ]
 
-  let ocaml_for_windows_packages ?cyg ?(extra = []) ?(version = "0.0.0.2") () =
+  let msvc_packages = [ "make"; "diffutils"; "patch"; "git" ]
+
+  let install_ocaml_for_windows ?cyg ?(version = "0.0.0.2") () =
     let packages =
-      "make" :: "diffutils" :: "mingw64-x86_64-gcc-g++" :: "vim" :: "git"
-      :: "curl" :: "rsync" :: "unzip" :: "patch" :: "m4" :: extra
+      [
+        "rsync";
+        "patch";
+        "diffutils";
+        "curl";
+        "make";
+        "unzip";
+        "git";
+        "m4";
+        "perl";
+      ]
     in
     let t =
       add

src-opam/windows.mli

@@ -122,11 +122,11 @@ module Cygwin : sig
   (** [msvc_packages] is the list of base development tools for the
       Caml MSVC port. *)
 
-  val ocaml_for_windows_packages :
-    ?cyg:cyg -> ?extra:string list -> ?version:string -> unit -> string list * t
-  (** [ocaml_for_windows_packages ?extra ()] returns the list of
-      Cygwin packages dependencies, and the installation instructions.
-      Extra packages may also be optionally supplied via [extra].
+  val install_ocaml_for_windows :
+    ?cyg:cyg -> ?version:string -> unit -> string list * t
+  (** [install_ocaml_for_windows ()] returns the list of Cygwin
+      packages dependencies, and the installation instructions for
+      OCaml for Windows.
       @see <https://fdopen.github.io/opam-repository-mingw/> *)
 
   val run_sh : ?cyg:cyg -> ('a, unit, string, t) format4 -> 'a