[issue23571] Raise SystemError if a function returns a result with an exception set

[STINNER Victor]

STINNER Victor added the comment:

> I believe that this patch exposes some subtle bugs in Django (see https://gist.github.com/berkerpeksag/8b8dbe594eb1a1c51275) and it would be great to add a note for third party libraries.

Berker, can you please rerun your test with my new commit to check if you see the function error in the error?

(I didn't update the doc yet, not investigated Antoine's suggestion, I will do that later.)

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