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/curlx/fopen.h

@@ -34,7 +34,7 @@
 int curlx_fseek(void *stream, curl_off_t offset, int whence);
 
 #ifdef _WIN32
-#include <sys/stat.h>  /* for _fstati64, struct _stati64 */
+#include <sys/stat.h>  /* for _fstati64(), struct _stati64 */
 #ifndef CURL_WINDOWS_UWP
 HANDLE curlx_CreateFile(const char *filename,
                         DWORD dwDesiredAccess,