dev-lang/perl useflags become a PERL_FEATURES use-expand

Title: dev-lang/perl useflags become a PERL_FEATURES use-expand
Author: Andreas K. Huettel <dilfridge@gentoo.org>
Posted: 2024-05-07
Revision: 2
News-Item-Format: 2.0

Starting with dev-lang/perl-5.38.2-r3, the three use flags "debug", 
"ithreads", and "quadmath" of Perl are renamed into a common
use-expand variable, PERL_FEATURES, which should be set *globally*
in make.conf.

If you do *not* want to change the settings of your Perl, make
sure that the new variable PERL_FEATURES contains the same settings
that were applied to your Perl all along. 

I.e., if you have dev-lang/perl[ithreads] installed, make sure
to now set in make.conf
  PERL_FEATURES="ithreads"

If you *want* to change the settings of your Perl, you may have to
run perl-cleaner after rebuilding dev-lang/perl:
  perl-cleaner --modules ; perl-cleaner --force --libperl

In either case, a full world update
  emerge -uDNav world
is recommended and should also bring your system into a consistent
state.

Background: This change in the structure of the useflags is
intended to solve bug 930123. The three useflags influence not only
how Perl itself is installed, but also all Perl modules...