perllocale: Update for 5.40 state of affairs

[khwilliamson]

This makes corrections, and additions

[jkeenan]

P.R. is failing t/porting/podcheck.t and short-circuiting CI tests. This patch should fix it.

diff --git a/pod/perllocale.pod b/pod/perllocale.pod
index e07e6e2696..31f17373f9 100644
--- a/pod/perllocale.pod
+++ b/pod/perllocale.pod
@@ -102,7 +102,7 @@ Perl runs.  This category is a POSIX extension, and Windows, for
 example, doesn't have it.  On systems without it, Perl uses workarounds
 to compensate.
 
-=head2 Category C<LC_ALL>
+=item Category C<LC_ALL>
 
 This is not an actual category, but a convenience short-hand to refer to
 all of the actual ones.

[leonerd]

Overall looks good. If you can address Jim's comments + the failing test we can pop this in for 5.40.

[khwilliamson]

This removes some text applicable to XS code only; I will soon add text to perlxs.pod to address that