gh-127604: Add C stack dumps to faulthandler

[ZeroIntensity]

This only adds it for glibc right now. I think it's possible to implement it for Windows with StackWalk64, but I'd prefer to get a solid working implementation for other systems before I dive into that.

• Issue: Add a way of printing a C backtrace to faulthandler #127604

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📚 Documentation preview 📚: https://cpython-previews--128159.org.readthedocs.build/en/128159/library/faulthandler.html#dumping-the-c-stack

[picnixz]

There are some PEP-7 nits but I don't know if this was done to be aligned with the rest of the code so you can freely ignore those nits.

[picnixz]

@ZeroIntensity If you ever use the web UI, don't forget to replace my tabs with spaces... hopefully your IDE does it but I see that I have tabs instead of spaces on my suggestions (I've corrected them but just double-check)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @ZeroIntensity for commit e79e661 🤖

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[jakkdl]

Nice! I did start playing around with an implementation myself, and looks like we made a couple different implementation decisions:

Instead of adding a dump_c_stack function, I added a kwarg to dump_traceback. I think I prefer your approach here, since a user may want to see the c backtrace but doesn't care about the python traceback. Though that does clash somewhat with it being a kwarg to enable (and register/dump_traceback_later).

I named my kwarg c_backtrace, though I think I prefer c_stack to avoid backtrace/traceback confusion.

I also added a kwarg to register(), and dump_traceback_later could also get it.

I made all functions raise an exception if passed c_stack=True and it wasn't available, and added a global faulthandler.HAS_C_BACKTRACE. I'm not sure what the best approach is here.