I found that fork + exec is the way perl spawns a sub-process, including on Windows. With this the keyboard interrupt will be sent to the subprocess as expected: 

my $child = fork();

if ($child)
{
    say 'Waiting';
    waitpid $child, 0;
    say 'Exiting'
}
else
{
    exec 'cmd', '/C', 'PowerShell', '-Command', 'sleep', '7', '&',
          'Echo', 'Done'
}

[download]
I suppose I still have to disable $SIG{'INT'} while waiting for the subprocess (that is, before the waitpid call), like system() does, but somehow I still want to receive the interrupt after the child process exits.

In reply to Re: Child process lingers after keyboard interrupt on Windows by toughy
in thread Child process lingers after keyboard interrupt on Windows by toughy

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