tidy-up: miscellaneous

- curl_ntlm_core, smtp, schannel: fix comments.
- curl_setup.h: fix to undef before define.
- tool_doswin, server/sockfilt: reduce variables scopes.
- tool_doswin: drop an interim variable.
- windows: replace `SOCKET_ERROR` with `0` to align with rest of code.
- libssh2: rename variable to align with rest of code.
- gtls, unit1398: use `#if 0`.
- curl_trc.h, curlx/inet_ntop.h: add missing parentheses in macro
  expressions.
- ldap.c: set empty macro to `do {} while(0)`.
- examples/crawler: rename a non-CURLcode `result` variable.
- CURLINFO_TLS_SESSION: drop stray colon.
- add `const` to casts where missing.
- drop unnecessary parentheses.
- fix indent.
- quote style.
- comment style.
- whitespace, newlines, fold/unfold.

Closes #20554

lib/asyn-ares.c

@@ -912,7 +912,7 @@ CURLcode Curl_async_ares_set_dns_local_ip4(struct Curl_easy *data)
   struct in_addr a4;
   const char *local_ip4 = data->set.str[STRING_DNS_LOCAL_IP4];
 
-  if((!local_ip4) || (local_ip4[0] == 0)) {
+  if(!local_ip4 || (local_ip4[0] == 0)) {
     a4.s_addr = 0; /* disabled: do not bind to a specific address */
   }
   else {
@@ -941,7 +941,7 @@ CURLcode Curl_async_ares_set_dns_local_ip6(struct Curl_easy *data)
   unsigned char a6[INET6_ADDRSTRLEN];
   const char *local_ip6 = data->set.str[STRING_DNS_LOCAL_IP6];
 
-  if((!local_ip6) || (local_ip6[0] == 0)) {
+  if(!local_ip6 || (local_ip6[0] == 0)) {
     /* disabled: do not bind to a specific address */
     memset(a6, 0, sizeof(a6));
   }