build: delete/replace clang warning pragmas

- delete redundant warning suppressions for `-Wformat-nonliteral`.
  This now relies on `CURL_PRINTF()` and it's theoratically possible
  that this macro isn't active but the warning is. We're ignoring this
  as a corner-case here.

- replace two pragmas with code changes to avoid the warnings.

Follow-up to aee4ebe591 #12803
Follow-up to 0923012758 #12540
Follow-up to 3829759bd0 #12489

Reviewed-by: Daniel Stenberg
Closes #12812

src/tool_easysrc.c

@@ -113,14 +113,7 @@ CURLcode easysrc_addf(struct slist_wc **plist, const char *fmt, ...)
   char *bufp;
   va_list ap;
   va_start(ap, fmt);
-#ifdef __clang__
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wformat-nonliteral"
-#endif
   bufp = curlx_mvaprintf(fmt, ap);
-#ifdef __clang__
-#pragma clang diagnostic pop
-#endif
   va_end(ap);
   if(!bufp) {
     ret = CURLE_OUT_OF_MEMORY;

src/tool_msgs.c

@@ -53,14 +53,7 @@ static void voutf(struct GlobalConfig *config,
     char *ptr;
     char *print_buffer;
 
-#ifdef __clang__
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wformat-nonliteral"
-#endif
     print_buffer = curlx_mvaprintf(fmt, ap);
-#ifdef __clang__
-#pragma clang diagnostic pop
-#endif
     if(!print_buffer)
       return;
     len = strlen(print_buffer);

src/tool_setopt.c

@@ -240,22 +240,11 @@ static char *c_escape(const char *str, curl_off_t len)
       if(p && *p)
         result = curlx_dyn_addn(&escaped, to + 2 * (p - from), 2);
       else {
-        const char *format = "\\x%02x";
-
-        if(len > 1 && ISXDIGIT(s[1])) {
-          /* Octal escape to avoid >2 digit hex. */
-          format = "\\%03o";
-        }
-
-#ifdef __clang__
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wformat-nonliteral"
-#endif
-        result = curlx_dyn_addf(&escaped, format,
+        result = curlx_dyn_addf(&escaped,
+                                /* Octal escape to avoid >2 digit hex. */
+                                (len > 1 && ISXDIGIT(s[1])) ?
+                                  "\\%03o" : "\\x%02x",
                                 (unsigned int) *(unsigned char *) s);
-#ifdef __clang__
-#pragma clang diagnostic pop
-#endif
       }
     }
   }