tidy-up: Markdown, clang-format nits

- drop leading indent from Markdown.
- switch to Markdown section markers where missing.
- move `&&` and `||` to the end of the line (C, Perl).
- openssl: add parenthesis to an if sub-expression.
- misc clang-format nits.
- unfold Markdown links.
- SSL-PROBLEMS.md: drop stray half code-fence.

Closes #20402

tests/pathhelp.pm

@@ -72,9 +72,9 @@ BEGIN {
 #
 {
     # Cached static variable, Perl 5.0-compatible.
-    my $is_win = $^O eq 'MSWin32'
-              || $^O eq 'cygwin'
-              || $^O eq 'msys';
+    my $is_win = $^O eq 'MSWin32' ||
+                 $^O eq 'cygwin' ||
+                 $^O eq 'msys';
 
     # Returns boolean true if OS is any form of Windows.
     sub os_is_win {