tidy-up: miscellaneous

- examples: sync debug output printf masks.
- INSTALL-CMAKE.md: tidy up section for some options.
- curl_sha512_256: delete comment suggesting an optimization.
- vtls/keylog: scope a variable.
- vtls/openssl: make a source code URL a permalink.
- vtls/schannel: drop redundant parentheses.
- test1119.pl: robustify `$1` -> `$s`.
- sync arg names in comments to match the code.
- tidy up and minor fixes to comments.
- fix formatting/indenting/comment/newline/include nits.
- move `UNITTEST` protos next to definitions, sync their argument names.
- make variables static.
- add parentheses to Perl `open()` calls.
- drop unnecessary double quotes in Perl.
- clang-format.

Closes #21000

lib/select.h

@@ -35,9 +35,7 @@
  * Definition of pollfd struct and constants for platforms lacking them.
  */
 
-#if !defined(HAVE_SYS_POLL_H) && \
-    !defined(HAVE_POLL_H) && \
-    !defined(POLLIN)
+#if !defined(HAVE_SYS_POLL_H) && !defined(HAVE_POLL_H) && !defined(POLLIN)
 
 #define POLLIN      0x01
 #define POLLPRI     0x02