tidy-up: comments, messages, formatting

- 'null-terminate', sync casing.
- add an `#endif` comment.
- avoid a few instances of 'will'.
- configure: 'aws' -> 'aws-sigv4', where missing.
- unfold/fold lines.
- update memzero/strzero comments.
- uppercase 'CRLF'.

Closes #22443

projects/OS400/os400sys.c

@@ -1035,4 +1035,4 @@ int Curl_os400_inflateEnd(z_streamp strm)
   return ret;
 }
 
-#endif
+#endif /* HAVE_LIBZ */

projects/vms/curl_crtl_init.c

@@ -126,7 +126,7 @@ static int sys_trnlnm(const char *logname, char *value, int value_len)
 
   if($VMS_STATUS_SUCCESS(status)) {
 
-    /* Null-terminate and return the string */
+    /* null-terminate and return the string */
     /*--------------------------------------*/
     value[result] = '\0';
   }