Parse compiler messages properly on Windows

[egorzhdan]

Currently SwiftPM dumps raw JSON data while compiling on Windows instead of the actual build status. This happens because JSONMessageStreamingParser splits the output lines by \n without taking \r into account on Windows.
After this change the compiler messages are parsed and displayed properly.

[egorzhdan]

cc @compnerd

[compnerd]

Thanks for identifying the issue!

What happens if it wants a raw carriage return? I suppose it will be escaped in the JSON right?

[egorzhdan]

Yeap, it gets escaped the same way as \n.

[compnerd]

Hmm, I wonder if there is a way to sink this lower so that when the processing is done, it splits on \r\n and \n.

[compnerd]

@swift-ci please test

[egorzhdan]

It's certainly possible, that would just be a bit more complex. This fix is simple and just works.
I can move the \r handling logic to the parsing stage though, if you think this is hacky.

[compnerd]

It definitely would be interesting to know how more complicated it is. If its not very complicated, that definitely would be nicer I think.