pcre2: preparation for libselinux-3.4

[Dominick Grift]

libselinux-3.4 added a change to encourage using pcre2 instead of pcre.

pcre has been unmaintained for quite some time but libselinux defaulted to using that.
for compatibility. Now libselinux-3.4 defaults to pcre2.

This set adds pcre2 to base, changes to official pcre2 upstream, updates pcre2 version to 10.40 and modifies pcre2 so that libselinux-3.4 can use it. When this set is merged we can update SELinux to version 3.4, remove pcre2 from the packages feed, remove legacy pcre from base and instead add it (back) to the packages feed.