checksrc: reduce directory-specific exceptions

By making them defaults, then fixing and/or reshuffling remaining
exceptions as necessary.

- checksrc: ban by default: `snprintf`, `vsnprintf`, `sscanf`, `strtol`.
- examples: replace `strtol` with `atoi` to avoid a checksrc exception.
- tests/libtest: replace `strtol` with `atol`.
- tests/server: replace most `strtol` with `atol`.
- tests/server: replace most `strtoul` with `atol`/`atoi`.
- tests/server: drop no longer used `util_ultous`.
- fix typo in checksrc rules: `vsnprint` -> `vsnprintf`.
- update local exceptions.

Also:
- examples: ban curl printf functions. They're discouraged in user code.
- examples: replace curl printf with system printf.
  Add `snprintf` workaround for <VS2015.
- examples/synctime: fix `-Wfloat-equal`.
- examples/synctime: exclude for non-Windows and non-UWP Windows.
- examples/synctime: build by default.

Closes #18823

docs/examples/cookie_interface.c

@@ -34,6 +34,10 @@
 #include <curl/curl.h>
 #include <curl/mprintf.h>
 
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#define snprintf _snprintf
+#endif
+
 static int print_cookies(CURL *curl)
 {
   CURLcode res;
@@ -93,10 +97,10 @@ main(void)
     printf("-----------------------------------------------\n"
            "Setting a cookie \"PREF\" via cookie interface:\n");
     /* Netscape format cookie */
-    curl_msnprintf(nline, sizeof(nline), "%s\t%s\t%s\t%s\t%.0f\t%s\t%s",
-                   ".example.com", "TRUE", "/", "FALSE",
-                   difftime(time(NULL) + 31337, (time_t)0),
-                   "PREF", "hello example, i like you!");
+    snprintf(nline, sizeof(nline), "%s\t%s\t%s\t%s\t%.0f\t%s\t%s",
+             ".example.com", "TRUE", "/", "FALSE",
+             difftime(time(NULL) + 31337, (time_t)0),
+             "PREF", "hello example, I like you!");
     res = curl_easy_setopt(curl, CURLOPT_COOKIELIST, nline);
     if(res != CURLE_OK) {
       fprintf(stderr, "Curl curl_easy_setopt failed: %s\n",
@@ -109,7 +113,7 @@ main(void)
        modified, likely not what you intended. For more information refer to
        the CURLOPT_COOKIELIST documentation.
     */
-    curl_msnprintf(nline, sizeof(nline),
+    snprintf(nline, sizeof(nline),
       "Set-Cookie: OLD_PREF=3d141414bf4209321; "
       "expires=Sun, 17-Jan-2038 19:14:07 GMT; path=/; domain=.example.com");
     res = curl_easy_setopt(curl, CURLOPT_COOKIELIST, nline);