Implement `putchar` so `Swift.print` works

[Finn Voorhees]

Will need changes in the Playdate SDK to support:
https://devforum.play.date/t/logtoconsole-without-a-linebreak/1819

@_silgen_name("putchar")
public func putchar(char: CInt) -> CInt {
    var char: [CChar] = [CChar(char), 0]
    System.log(&char)
    return 0
}