Porting/bisect.pl: Add missing full stop
Stop anon sub compilation from clobbering __ANON__

Anonymous subs point to *__ANON__ simply because internals expect
defined subroutines to have CvGV pointing somewhere.

So why does anonymous constant sub compilation wipe
*__ANON__{CODE} clean?

$ perl -e 'sub main::__ANON__ { 42 }; warn main::__ANON__; # sub(){3}'
42 at -e line 1.
$ perl -e 'sub main::__ANON__ { 42 }; warn main::__ANON__;  sub(){3}'
Undefined subroutine &main::__ANON__ called at -e line 1.

It doesn’t happen with non-constant subs:

$ perl -e 'sub main::__ANON__ { 42 }; warn main::__ANON__;  sub{3}'
42 at -e line 1.

This is actually a regression:

../perl.git/Porting/bisect.pl  --end=perl-5.8.8  --target=miniperl -e  'sub main::__ANON__ { 42 }; warn main::__ANON__;  sub(){3}'

beab0874143b7208922720fecefc4a224011fa25 is the first bad commit
commit beab0874143b7208922720fecefc4a224011fa25
Author: John Tobey <jtobey at john-edwin-tobey.org>
Date:   Fri Oct 20 18:03:27 2000 -0400

    Re: Creating const subs for constants.
    Message-Id: <m13mo0N-000FObC@feynman.localnet>

    p4raw-id: //depot/perl@7389

The new code path for constants did an unconditional
GvCV_set(gv, NULL), instead of checking whether there was a
name first.
Stop prototype declaration from clobbering constants

$ perl -e 'use constant f=>3; sub f($); warn eval "&f"'
Runaway prototype at -e line 1.
Prototype mismatch:: none vs ($) at -e line 1.
Undefined subroutine &main::f called at (eval 1) line 1.
	...caught at -e line 1.
$ perl -e 'sub f (){3} sub f($); warn eval "&f"'
Prototype mismatch: sub main::f () vs ($) at -e line 1.
3 at -e line 1.

(The ‘Runaway prototype’ warning was removed in acfcf464b177, in which
I stated wrongly that the warning could only come about with stash
manipulation.  I suppose the warning was really warning me that the
implementation was broken, which it was until this commit.)

When constant refs in the symbol table were introduced in 5.10.0
(a bisect points to e040ff70dc), one code path in newATTRSUB--that
assumes that a stash entry that is not a GV is not a defined sub,
but either a forward declaration or no sub at all--was not updated to
account for this new way of storing constants.
perldelta for #80368/e4916dd1b3
perldelta for eff754733a9
perldelta for acb187b49 (part of #69456)
perldelta for 8380b6901
perldelta: A to-do item

Mostly my own reminder, because I have not rebased yet, and this
entry will conflict with something already pushed.
perldelta for 4dda930be/#122556
perldelta for f20d0df0f
perldelta for 211a4342
perldelta for 8b57a5fa