gh-112075: Add gc shared bits

[DinoV]

This adds the GC shared flags for objects to the gc bit states in free-threaded builds. This will allow marking objects as being shared so that we can use QSBR to free them, enabling lock-free readers for dict (and other) objects.

• Issue: Make dict objects thread-safe in --disable-gil builds #112075

[colesbury]

LGTM!

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86-64 macOS 3.x has failed when building commit bcccf1f.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/366/builds/6539) and take a look at the build logs.
4. Check if the failure is related to this commit (bcccf1f) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/366/builds/6539

Failed tests:

• test.test_multiprocessing_forkserver.test_processes

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 9, done. remote: Counting objects: 11% (1/9) remote: Counting objects: 22% (2/9) remote: Counting objects: 33% (3/9) remote: Counting objects: 44% (4/9) remote: Counting objects: 55% (5/9) remote: Counting objects: 66% (6/9) remote: Counting objects: 77% (7/9) remote: Counting objects: 88% (8/9) remote: Counting objects: 100% (9/9) remote: Counting objects: 100% (9/9), done. remote: Compressing objects: 20% (1/5) remote: Compressing objects: 40% (2/5) remote: Compressing objects: 60% (3/5) remote: Compressing objects: 80% (4/5) remote: Compressing objects: 100% (5/5) remote: Compressing objects: 100% (5/5), done. remote: Total 5 (delta 4), reused 0 (delta 0), pack-reused 0 
From https://github.com/python/cpython
* branch main -> FETCH_HEAD
Note: switching to 'bcccf1fb63870c1b7f8abe246e27b7fff343abd7'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
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do so (now or later) by using -c with the switch command. Example:
git switch -c <new-branch-name>
Or undo this operation with:
git switch -
Turn off this advice by setting config variable advice.detachedHead to false
HEAD is now at bcccf1fb63 gh-112075: Add gc shared bits (#114931)
Switched to and reset branch 'main'
configure: WARNING: pkg-config is missing. Some dependencies may not be detected correctly./Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: libpython3.13d.a(dynamic_annotations.o) has no symbols/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: libpython3.13d.a(gc_free_threading.o) has no symbols/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: libpython3.13d.a(jit.o) has no symbolsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsld: warning: -undefined dynamic_lookup may not work with chained fixupsmake: *** [buildbottest] Error 2

[vstinner]

See issue gh-115124: AMD64 Windows11 Bigmem 3.x: test_bigmem failed with !_Py_IsImmortal(FROM_GC(gc)) assertion error. PR #114931 or PR #108038 caused a regression.