sysprep: Make a common Utils.compare_command_line_args function.

This isn't quite code motion, since the new function also ignores case
(which previously we didn't ignore).

sysprep/sysprep_operation.ml

@@ -138,10 +138,8 @@ let dump_pod_options () =
       | Arg.Rest _ -> assert false (* XXX not implemented *)
   ) args in
 
-  let args = List.sort (
-    fun (a, _) (b, _) ->
-      compare (skip_dashes a) (skip_dashes b)
-  ) args in
+  let args =
+    List.sort (fun (a, _) (b, _) -> compare_command_line_args a b) args in
 
   List.iter (
     fun (arg_name, (op_name, heading, pod)) ->

sysprep/utils.ml

@@ -81,3 +81,6 @@ let skip_dashes str =
   let i = loop 0 in
   if i = 0 then str
   else String.sub str i (n-i)
+
+let compare_command_line_args a b =
+  compare (String.lowercase (skip_dashes a)) (String.lowercase (skip_dashes b))

sysprep/utils.mli

@@ -44,3 +44,8 @@ val skip_dashes : string -> string
 
     If the string contains only dash characters, this raises
     [Invalid_argument "skip_dashes"]. *)
+
+val compare_command_line_args : string -> string -> int
+(** Compare two command line arguments (eg. ["-a"] and ["--V"]),
+    ignoring leading dashes and case.  Note this assumes the
+    strings are 7 bit ASCII. *)