Add default interrupt handlers

[straight-shoota]

Resolves #8687

[HertzDevil]

On Windows this works when run alone:

lib LibC
  fun GenerateConsoleCtrlEvent(dwCtrlEvent : DWORD, dwProcessGroupId : DWORD) : BOOL
end

at_exit { print "Exiting" }
print "."
STDOUT.flush
LibC.GenerateConsoleCtrlEvent(LibC::CTRL_C_EVENT, 0)
sleep

However it also sends Ctrl+C to the spec process itself, effectively aborting the spec. SIGBREAK might be possible to test but that requires passing CREATE_NEW_PROCESS_GROUP to CreateProcessW

[straight-shoota]

I suppose we could put that in spec/manual.

[straight-shoota]

Even a manual spec needs a functioning spec harness which doesn't work when the process gets cancelled from inside an example.
So I added the code only in a comment next to the other specs. That should be good enough.

[HertzDevil]

It should be noted that restore_interrupts! does not restore this default interrupt handler (or maybe it should?)

[straight-shoota]

This was eventually reverted in #13673 due to complications mentioned in #13672