Restore basic debugging support on Linux.

[Apprentice-Alchemist]

It doesn't work perfectly yet (for example stepping in/out is still broken), but at least breakpoints and breaking on exceptions works again.

[ncannasse]

That seems overly complex. Why allowing several debuggers to connect ?

[rcstuber]

I think we should reopen and discuss this PR!
It looks valid for future Hashlink on ARM which is currently a work-in-progress by @Apprentice-Alchemist

[Jarrio]

That seems overly complex. Why allowing several debuggers to connect ?

It's been a while since I wrote the code, but iirc the whole background thread and condition variable dance is needed because there's no way (that I found) to waitpid with a timeout.

[Apprentice-Alchemist]

That seems overly complex. Why allowing several debuggers to connect ?

It's been a while since I wrote the code, but iirc the whole background thread and condition variable dance is needed because there's no way (that I found) to waitpid with a timeout.

@Jarrio I was talking about my new implementation, not this one.