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

tests/runner.pm

@@ -666,7 +666,7 @@ sub singletest_setenv {
         if($s =~ /([^=]*)(.*)/) {
             my ($var, $content) = ($1, $2);
             # remember current setting, to restore it once test runs
-            $oldenv{$var} = ($ENV{$var})?"$ENV{$var}":'notset';
+            $oldenv{$var} = ($ENV{$var}) ? "$ENV{$var}" : 'notset';
 
             if($content =~ /^=(.*)/) {
                 # assign it