Issue Description:

When running Swift 4.1 on Linux, running the interpreter with the following results in a crash:

$ export C_INCLUDE_PATH=/usr/lib/swift/clang/include
$ export CPLUS_INCLUDE_PATH=$C_INCLUDE_PATH
$ swift
Welcome to Swift version 4.1 (swift-4.1-RELEASE). Type :help for assistance.
1> import Foundation
2> NSRegularExpression(pattern:"(.*)",options:[])
$R0: Foundation.NSRegularExpression = {
Foundation.NSObject = {}
Segmentation fault

Modifying to store the return value does not have this effect:

$ swift
Welcome to Swift version 4.1 (swift-4.1-RELEASE). Type :help for assistance.
1> import Foundation
2> _ = NSRegularExpression(pattern:"(.*)",options:[])
3> ^D

If the value is stored to an intermediate value, then printed, the error is seen:

swift
Welcome to Swift version 4.1 (swift-4.1-RELEASE). Type :help for assistance.
1> import Foundation
2> let a = NSRegularExpression(pattern:"(.*)",options:[])
a: Foundation.NSRegularExpression = {
Foundation.NSObject = {}
Segmentation fault

However, if the value is printed (with print or debugPrint) then we don't see the issue:

3> debugPrint(NSRegularExpression(pattern:"(.*)",options:[]))
<NSRegularExpression: 0x0000555555599ca0>
4> print(NSRegularExpression(pattern:"(.*)",options:[]))
<NSRegularExpression: 0x0000555555599ca0>
5>

So there is something in the way that the interpreter is trying to unpack or display the result that's causing the segfault.

Created on an Ubuntu runtime with Swift 4.1 release.