Get rid off dependency on Signal in Win32 Process::Status

[jan-zajic]

Remove dependency on Signal on win32 platform.

[straight-shoota]

I'd like to see a comment for each location that is removed which explains why this doesn't work for win32, whether that's a problem and if this needs attention later.

[ysbaddaden]

Maybe we can have a minimal Signal enum on Win32 (with a TODO: implement signals on Win32), then make Process::Status.exit_signal return a dummy Process::Status.new(-1). That would allow to keep the status.exit_signal usages —or wrap/guard them with if status.signal_exit?.

Signal exit is only useful on POSIX, but a dummy is harmless and transparent on Win32, so developers don't have to deal with platform discrepancies.

[RX14]

Yeah, I'd much rather add something to the windows stubs file than ifdef out code. Ifdefs should be kept to a minimum.

[straight-shoota]

The result of #8647 is also relevant for this.