Open Radar

 
Summary:
Sometimes when attempting to po variables with lldb in Swift, it fails with this error:

```
error: in auto-import:
failed to get module '<redacted>' from AST context:
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "UIKitOverlayShims.h"
        ^

error: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/shims/UIKitOverlayShims.h:24:11: error: use of undeclared identifier 'UIFocusSystem'
  return [UIFocusSystem environment:environment containsEnvironment:otherEnvironment];
          ^

error: could not build Objective-C module '_SwiftUIKitOverlayShims'
```

Steps to Reproduce:
1. Set a breakpoint in a Swift project
2. At the breakpoint run `po self`

Expected Results:
lldb prints the description of self

Actual Results:
It fails with this error

Version:
Xcode 9.0 9A235

Notes:
Here's a discussion on the developer forums about this issue: https://forums.developer.apple.com/thread/84400

The workaround of editing /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/shims to remove the UIFocusSystem call seems to work, although one time lldb also crashed when doing this, attached is the report hoping that might be useful for this or another issue.