Importing Foundation or Glibc in REPL on Ubuntu 16.10 failing

Using the Ubuntu 16.10 snapshot from 15 December (or a build from
master) I can't seem to get "import Foundation" or "import Glibc"
working in the REPL. Here's an example:

-----------------8<------------------
$ swift
Welcome to Swift version 3.1-dev (LLVM 7d4a331ed3, Clang d8c33dc710,
Swift 2ea7951d05). Type :help for assistance.
  1> import Glibc
<module-includes>:3:10: note: in file included from <module-includes>:3:
#include "///usr/include/utmp.h"
         ^

///usr/include/utmp.h:23:10: note: in file included from
///usr/include/utmp.h:23:
#include <sys/types.h>
         ^

error: /usr/include/x86_64-linux-gnu/sys/types.h:146:10: error:
'stddef.h' file not found
#include <stddef.h>
         ^

error: could not build Objective-C module 'SwiftGlibc'
-----------------8<------------------

This works fine if I use 'swiftc' and compile a file:

$ cat x.swift
import Glibc

print(random())

$ swiftc x.swift
$ ./x
...
-----------------8<------------------

If I explicitly pass include paths to 'swift' it works in the REPL:

-----------------8<------------------
$ swift -I/home/user/swift-install/usr/lib/swift/clang/include/
-I/home/user/swift-install/usr/include/lldb/Symbol/
Welcome to Swift version 3.1-dev (LLVM 7d4a331ed3, Clang d8c33dc710,
Swift 2ea7951d05). Type :help for assistance.
  1> import Glibc
  2> random()
$R0: Int = 1804289383
-----------------8<------------------

Is there some setting or installation setup step I'm missing?

···

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