PATCH: [perl #90646] perlop.pod: Clarify & | and ^ binary operations
POSIX.pod: Nits

Most of the changes are to add C<> around code snippets, like function
macro and constant names.

There are a couple of grammar changes.

The only sort-of substantive change is that strtod() does respect
setlocale.  Previously it said it *should* respect setlocale.
PerlIO.pm: Make pod :utf8 caution more prominent

The :utf8 layer continues to have security issues.  This moves the
warning about that to earlier where it's more likely to be seen, and
makes it stand out more.