Issue #10089: Add support for arbitrary -X options on the command-line.

They can be retrieved through a new attribute `sys._xoptions`.

Python/getopt.c

@@ -89,12 +89,6 @@ int _PyOS_GetOpt(int argc, wchar_t **argv, wchar_t *optstring)
         return '_';
     }
 
-    if (option == 'X') {
-        fprintf(stderr,
-          "-X is reserved for implementation-specific arguments\n");
-        return '_';
-    }
-
     if ((ptr = wcschr(optstring, option)) == NULL) {
         if (_PyOS_opterr)
           fprintf(stderr, "Unknown option: -%c\n", (char)option);