34099797: ibtool should allow treating warnings as errors

[openradar-mirror]

Description

Summary: Currently if a Interface Builder warning is introduced, there is no supported way to fail the build entirely. It would be useful if there was an Xcode build setting / ibtool flag for enabling this behavior, similar to SWIFT_TREAT_WARNINGS_AS_ERRORS.

Steps to Reproduce:

1. Create a new project
2. Create a storyboard
3. In the storyboard add a label
4. Add constraints to the label such that the layout is ambiguous
5. Build

Expected Results: There is some way to make the produced warning fail the build

Actual Results: A warning is produced, but the build (or archive) succeeds

Version: Xcode 9 beta 6

Notes: See the attached project for an example of an Interface Builder warning that would case a failure in this case

- Product Version: Xcode 9 beta 6 Created: 2017-08-27T00:20:29.915010 Originated: 2017-08-26T20:20:00 Open Radar Link: http://www.openradar.me/34099797

[openradar-mirror]

Modified: 2017-08-29T01:53:45.593510

[openradar-mirror]

Modified: 2017-08-29T01:53:45.593510

[openradar-mirror]

Modified: 2017-08-29T01:53:45.593510