Reproducing steps:
1. launch Swift REPL in terminal
2. paste `enum 🤔 { case 👶🏻, 👴🏻 }`
3. exit Swift REPL
4. launch Swift REPL again

Actual log:
```terminal.session
➜  11:48:39  TOOLCHAINS=org.swift.3020170323a swift
Welcome to Apple Swift version 3.1-dev (LLVM a95654d887, Clang 4a3ce873fe, Swift 3061ba06f8). Type :help for assistance.
  1> enum \U+1F914 { case 👶\U+1F3FB, 👴\U+1F3FB }
  2> :exit
➜  11:49:51  TOOLCHAINS=org.swift.3020170323a swift
Welcome to Apple Swift version 3.1-dev (LLVM a95654d887, Clang 4a3ce873fe, Swift 3061ba06f8). Type :help for assistance.
[1]    74353 segmentation fault  TOOLCHAINS=org.swift.3020170323a swift
```