Correctly handle should_panic doctest attribute

[GuillaumeGomez]

Fixes #143009.

Instead of checking the exit code, we directly wrap the doctest code with catch_unwind and if a panic happened, then we return success for the test, otherwise we display the appropriate error message.

I think last one who reviewed doctest changes was @fmease so setting you as reviewer. :)

r? fmease

[rustbot]

fmease is not on the review rotation at the moment.
They may take a while to respond.

[rustbot]

This PR modifies run-make tests.

cc @jieyouxu

[GuillaumeGomez]

Ah, someone else then (sorry for the ping).

r? notriddle

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

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[purplesyringa]

I don't like this: this causes std::process::exit(0); to be considered as a successfully passed test, and fn main() { panic!(); } is treated as an error rather than a panic.