[Perl/perl5] a556b8: getpgrp: getpgid used for PID != 0 is now a lot mo...

[Tony Cook via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: a556b8328585fddac7a04424973308a894687234
      
https://github.com/Perl/perl5/commit/a556b8328585fddac7a04424973308a894687234
  Author: Tony Cook <t...@develop-help.com>
  Date:   2023-07-20 (Thu, 20 Jul 2023)

  Changed paths:
    M perl.h
    M pod/perlfunc.pod

  Log Message:
  -----------
  getpgrp: getpgid used for PID != 0 is now a lot more portable

POSIX.1 2004 lists getpgid as an XSI extension, 2017 edition lists
it as BASE.

Removed the comments since it now seems irrelevant.

Fixes #19648