Creating subprocess breaks signal handling

[d1rewolf]

Crystal 0.23.1 [e2a1389] (2017-07-13) LLVM 3.8.1
Ubuntu 17.04

The following code will never make it to 'puts "3"':

chan = Channel(Int32).new

Signal::INT.trap {
    puts "Got INT signal..."
        puts "1"
        puts "2"
        `sleep 1`
        puts "3"
        `sleep 1`
        puts "4"
        `sleep 1`
        puts "Done..."
}
puts "Receiving"
chan.receive         

Removing the `` calls will allow it to finish the block.