Sketches that includes String objects did not compile, so simply copy the wstring.cpp from Teensy3 directory.

Likewise sketches that used stream functions like:
Serial1.readBytes would not compile as the Stream  sources were not included.

So  likewise copied over from Teensy3 directory

https://forum.pjrc.com/threads/41282-Strange-looking-limit-checks-in-Teensy3-Version-of-Stream-cpp