protoc-c: Silence compilers that complain about sprintf()

protoc-c/c_helpers.cc

@@ -526,7 +526,7 @@ static int CEscapeInternal(const char* src, int src_len, char* dest,
         if (!isprint(*src) || (last_hex_escape && isxdigit(*src))) {
           if (dest_len - used < 4) // need space for 4 letter escape
             return -1;
-          sprintf(dest + used, (use_hex ? "\\x%02x" : "\\%03o"),
+          snprintf(dest + used, dest_len - used, (use_hex ? "\\x%02x" : "\\%03o"),
                   static_cast<uint8>(*src));
           is_hex_escape = use_hex;
           used += 4;