tool: support UTF-16 command line on Windows

- use `wmain` instead of `main` when `_UNICODE` is defined [0]
- define `argv_item_t` as `wchar_t *` in this case
- use the curl_multibyte gear to convert the command-line arguments to
  UTF-8

This makes it possible to pass parameters with characters outside of
the current locale on Windows, which is required for some tests, e.g.
the IDN tests. Out of the box, this currently only works with the
Visual Studio project files, which default to Unicode, and winbuild
with the `ENABLE_UNICODE` option.

[0] https://devblogs.microsoft.com/oldnewthing/?p=40643

Ref: https://github.com/curl/curl/issues/3747
Closes https://github.com/curl/curl/pull/3784

lib/curl_setup_once.h

@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -481,6 +481,8 @@ typedef int sig_atomic_t;
 
 #ifdef __VMS
 #define argv_item_t  __char_ptr32
+#elif defined(_UNICODE)
+#define argv_item_t wchar_t *
 #else
 #define argv_item_t  char *
 #endif

src/tool_getparam.c

@@ -2248,20 +2248,22 @@ ParameterError parse_args(struct GlobalConfig *global, int argc,
   struct OperationConfig *config = global->first;
 
   for(i = 1, stillflags = TRUE; i < argc && !result; i++) {
-    orig_opt = argv[i];
+    orig_opt = curlx_convert_tchar_to_UTF8(argv[i]);
 
-    if(stillflags && ('-' == argv[i][0])) {
+    if(stillflags && ('-' == orig_opt[0])) {
       bool passarg;
-      char *flag = argv[i];
 
-      if(!strcmp("--", argv[i]))
+      if(!strcmp("--", orig_opt))
         /* This indicates the end of the flags and thus enables the
            following (URL) argument to start with -. */
         stillflags = FALSE;
       else {
-        char *nextarg = (i < (argc - 1)) ? argv[i + 1] : NULL;
+        char *nextarg = (i < (argc - 1))
+          ? curlx_convert_tchar_to_UTF8(argv[i + 1])
+          : NULL;
 
-        result = getparameter(flag, nextarg, &passarg, global, config);
+        result = getparameter(orig_opt, nextarg, &passarg, global, config);
+        curlx_unicodefree(nextarg);
         config = global->last;
         if(result == PARAM_NEXT_OPERATION) {
           /* Reset result as PARAM_NEXT_OPERATION is only used here and not
@@ -2297,7 +2299,7 @@ ParameterError parse_args(struct GlobalConfig *global, int argc,
       bool used;
 
       /* Just add the URL please */
-      result = getparameter((char *)"--url", argv[i], &used, global,
+      result = getparameter("--url", orig_opt, &used, global,
                             config);
     }
   }
@@ -2314,5 +2316,6 @@ ParameterError parse_args(struct GlobalConfig *global, int argc,
       helpf(global->errors, "%s\n", reason);
   }
 
+  curlx_unicodefree(orig_opt);
   return result;
 }

src/tool_main.c

@@ -273,22 +273,28 @@ static void restore_terminal(void)
 /*
 ** curl tool main function.
 */
+#ifdef _UNICODE
+int wmain(int argc, wchar_t *argv[])
+#else
 int main(int argc, char *argv[])
+#endif
 {
   CURLcode result = CURLE_OK;
   struct GlobalConfig global;
   memset(&global, 0, sizeof(global));
 
 #ifdef WIN32
+#ifdef _tcscmp
   /* Undocumented diagnostic option to list the full paths of all loaded
      modules. This is purposely pre-init. */
-  if(argc == 2 && !strcmp(argv[1], "--dump-module-paths")) {
+  if(argc == 2 && !_tcscmp(argv[1], _T("--dump-module-paths"))) {
     struct curl_slist *item, *head = GetLoadedModulePaths();
     for(item = head; item; item = item->next)
       printf("%s\n", item->data);
     curl_slist_free_all(head);
     return head ? 0 : 1;
   }
+#endif /* _tcscmp */
   /* win32_init must be called before other init routines. */
   result = win32_init();
   if(result) {

src/tool_operate.c

@@ -2427,6 +2427,7 @@ static CURLcode run_all_transfers(struct GlobalConfig *global,
 CURLcode operate(struct GlobalConfig *global, int argc, argv_item_t argv[])
 {
   CURLcode result = CURLE_OK;
+  char *first_arg = curlx_convert_tchar_to_UTF8(argv[1]);
 
   /* Setup proper locale from environment */
 #ifdef HAVE_SETLOCALE
@@ -2435,8 +2436,8 @@ CURLcode operate(struct GlobalConfig *global, int argc, argv_item_t argv[])
 
   /* Parse .curlrc if necessary */
   if((argc == 1) ||
-     (!curl_strequal(argv[1], "-q") &&
-      !curl_strequal(argv[1], "--disable"))) {
+     (!curl_strequal(first_arg, "-q") &&
+      !curl_strequal(first_arg, "--disable"))) {
     parseconfig(NULL, global); /* ignore possible failure */
 
     /* If we had no arguments then make sure a url was specified in .curlrc */
@@ -2446,6 +2447,8 @@ CURLcode operate(struct GlobalConfig *global, int argc, argv_item_t argv[])
     }
   }
 
+  curlx_unicodefree(first_arg);
+
   if(!result) {
     /* Parse the command line arguments */
     ParameterError res = parse_args(global, argc, argv);