readLine() is implemented in InputStream.swift, and it contains following comment.
// FIXME: Unicode conformance. To fix this, we need to reimplement the
// code we call above to get a line, since it will only stop on LF.
// <rdar://problem/20013999> Recognize Unicode newlines in readLine()
// Recognize only LF and CR+LF combinations for now.
I cannot access rdar://problem/*, so posted here.