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First reported at https://github.com/numpy/numpy/issues/18720
After upgrading to Python 3.9.3, 32-bit on Windows, importing numpy (installed via `pip install numpy`) crashes:
```
Microsoft Windows [Version 10.0.19041.906]
C:\Python39-32>python -X dev
Python 3.9.3 (tags/v3.9.3:e723086, Apr 2 2021, 11:01:03) [MSC v.1928 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy
Windows fatal exception: access violation
Current thread 0x0000105c (most recent call first):
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap_external>", line 1116 in exec_module
 File "<frozen importlib._bootstrap>", line 680 in _load_unlocked
 File "<frozen importlib._bootstrap>", line 986 in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 1007 in _find_and_load
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap_external>", line 1116 in exec_module
 File "<frozen importlib._bootstrap>", line 680 in _load_unlocked
 File "<frozen importlib._bootstrap>", line 986 in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 1007 in _find_and_load
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap_external>", line 1116 in exec_module
 File "<frozen importlib._bootstrap>", line 680 in _load_unlocked
 File "<frozen importlib._bootstrap>", line 986 in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 1007 in _find_and_load
 File "C:\Python39-32\lib\site-packages\numpy\random\_pickle.py", line 1 in <module>
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap_external>", line 790 in exec_module
 File "<frozen importlib._bootstrap>", line 680 in _load_unlocked
 File "<frozen importlib._bootstrap>", line 986 in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 1007 in _find_and_load
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap>", line 1058 in _handle_fromlist
 File "C:\Python39-32\lib\site-packages\numpy\random\__init__.py", line 179 in <module>
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap_external>", line 790 in exec_module
 File "<frozen importlib._bootstrap>", line 680 in _load_unlocked
 File "<frozen importlib._bootstrap>", line 986 in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 1007 in _find_and_load
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap>", line 1058 in _handle_fromlist
 File "C:\Python39-32\lib\site-packages\numpy\__init__.py", line 156 in <module>
 File "<frozen importlib._bootstrap>", line 228 in _call_with_frames_removed
 File "<frozen importlib._bootstrap_external>", line 790 in exec_module
 File "<frozen importlib._bootstrap>", line 680 in _load_unlocked
 File "<frozen importlib._bootstrap>", line 986 in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 1007 in _find_and_load
 File "<stdin>", line 1 in <module>
```
Rebuilding numpy from source against Python 3.9.3 fixes this crash, but many other packages compiled against older versions of Python 3.9.x still crash.
I think this might be due to <https://github.com/python/cpython/commit/8b795ab5541d8a4e69be4137dfdc207714270b77#diff-7285576bdacf86fe37274d3d0d399c29b4be2959005f60ac0729615d8fca9186>.
In `bpo-42500: Fix recursion in or after except (GH-23568) (#24501)`, the public `PyThreadState` struct changed. This breaks ABI compatibility for code that is directly accessing the `PyThreadState` struct members, which is not uncommon. E.g. in Cython <https://github.com/cython/cython/blob/0.29.x/Cython/Utility/Exceptions.c#L93-L115>. This code will fail on 32-bit. On 64-bit it passes because of fortunate struct alignment AFAICT.

Tomorrow evening CEST (around 30 hours from now) I intend to release a hotfix 3.9.4 with Mark's fix.

I really suggest a simple rollback (revert) of the change rather than a redo-fix for 3.9.4. Unless you like the idea of a possible 3.9.5 if the redo-fix itself has issues that haven't been given due thought in the rush to undo the 3.9.3 mistake.
This leaves more time for a proper fix of bpo-42500 in 3.9 not crafted under duress.

New changeset c7b0feca25fc68ec3e0884b82e5f45a4da011e8e by Gregory P. Smith in branch '3.9':
[3.9] bpo-43710: Rollback the 3.9 bpo-42500 fix, it broke the ABI in 3.9.3 (#25179)
https://github.com/python/cpython/commit/c7b0feca25fc68ec3e0884b82e5f45a4da011e8e

Thank you for fixing this issue so fast! Python 3.9.4 works well.