When trying to initialize a `CharacterSet` using `(charactersIn: String)`, the application crashes with a seg fault if the string contains 64 or more characters. It doesn't seem to matter what characters are included.
The issue occurs on Ubuntu 16.04 (haven't tested other versions) but does NOT occur on macOS.
Tested on Swift 3.0.1 Release and swift-DEVELOPMENT-SNAPSHOT-2016-11-12-a-ubuntu16.04
Steps to reproduce in REPL:
>> Execution interrupted.