Replace the dependency on GNU patch by a strict dependency on git

src/client/opamInitDefaults.ml

@@ -55,9 +55,6 @@ let not_open_free_bsd_filter =
 let win32_filter = os_filter "win32"
 let sandbox_filter = FOr (linux_filter, macos_filter)
 
-let gpatch_filter = FOr (openbsd_filter, freebsd_filter)
-let patch_filter = FNot gpatch_filter
-
 let gtar_filter = openbsd_filter
 let tar_filter = FNot gtar_filter
 
@@ -132,8 +129,7 @@ let required_tools ~sandboxing () =
   req_dl_tools () @
   [
     ["diff"], None, None;
-    ["patch"], None, Some patch_filter;
-    ["gpatch"], None, Some gpatch_filter;
+    ["git"], None, None;
     ["tar"], None, Some tar_filter;
     ["gtar"], None, Some gtar_filter;
     ["unzip"], None, None;

src/core/opamSystem.ml

@@ -1590,13 +1590,7 @@ let patch ?(preprocess=true) ~dir p =
     else
       p
   in
-  let patch_cmd =
-    match OpamStd.Sys.os () with
-    | OpamStd.Sys.OpenBSD
-    | OpamStd.Sys.FreeBSD -> "gpatch"
-    | _ -> "patch"
-  in
-  make_command ~name:"patch" ~dir patch_cmd ["-p1"; "-i"; p'] @@> fun r ->
+  make_command ~name:"git apply" ~dir "git" ["apply"; "-p1"; p'] @@> fun r ->
     if not (OpamConsole.debug ()) then Sys.remove p';
     if OpamProcess.is_success r then Done None
     else Done (Some (Process_error r))