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

docs/examples/crawler.c

@@ -131,18 +131,18 @@ static size_t follow_links(CURLM *multi, struct memory *mem, const char *url)
   xmlChar *xpath;
   xmlNodeSetPtr nodeset;
   xmlXPathContextPtr context;
-  xmlXPathObjectPtr result;
+  xmlXPathObjectPtr object;
   if(!doc)
     return 0;
   xpath = (xmlChar *)"//a/@href";
   context = xmlXPathNewContext(doc);
-  result = xmlXPathEvalExpression(xpath, context);
+  object = xmlXPathEvalExpression(xpath, context);
   xmlXPathFreeContext(context);
-  if(!result)
+  if(!object)
     return 0;
-  nodeset = result->nodesetval;
+  nodeset = object->nodesetval;
   if(xmlXPathNodeSetIsEmpty(nodeset)) {
-    xmlXPathFreeObject(result);
+    xmlXPathFreeObject(object);
     return 0;
   }
   count = 0;
@@ -167,7 +167,7 @@ static size_t follow_links(CURLM *multi, struct memory *mem, const char *url)
     }
     xmlFree(link);
   }
-  xmlXPathFreeObject(result);
+  xmlXPathFreeObject(object);
   return count;
 }
 

docs/examples/sessioninfo.c

@@ -38,6 +38,7 @@
 #include <stdio.h>
 
 #include <curl/curl.h>
+
 #include <gnutls/gnutls.h>
 #include <gnutls/x509.h>
 

docs/examples/smooth-gtk-thread.c

@@ -34,7 +34,6 @@
  * gcc -ggdb `pkg-config --cflags  --libs gtk+-2.0` -lcurl -lssl -lcrypto
  *   -lgthread-2.0 -dl  smooth-gtk-thread.c -o smooth-gtk-thread
  */
-
 #include <stdio.h>
 #include <gtk/gtk.h>
 #include <glib.h>

docs/examples/unixsocket.c

@@ -26,6 +26,7 @@
  * </DESC>
  */
 #include <stdio.h>
+
 #include <curl/curl.h>
 
 #ifdef USE_ABSTRACT

docs/examples/usercertinmem.c

@@ -39,10 +39,10 @@
 
 #include <openssl/ssl.h>
 
-#include <curl/curl.h>
-
 #include <stdio.h>
 
+#include <curl/curl.h>
+
 #if defined(__GNUC__) || defined(__clang__)
 #pragma GCC diagnostic ignored "-Woverlength-strings"
 #endif

docs/examples/websocket-updown.c

@@ -27,6 +27,7 @@
  */
 #include <stdio.h>
 #include <string.h>
+
 #include <curl/curl.h>
 
 static size_t write_cb(char *b, size_t size, size_t nitems, void *p)