TestSupport will not build on Ubuntu 14

[vikingjs]

When trying to build my project on a heroku-like remote server I don't control, I get a bunch of errors similar to this:

/build/app/.build/release/TestSupport.build/Fixtures.swift.o:/build/app/.build/release/TestSupport.build/Fixtures.swift.o:_TMfC11TestSupport22CustomExecutorTestCase: error: undefined reference to 'TFC6XCTest6XCTestg7testRunGSqCS_9XCTestRun'

I'm unable to (simply) remove TestSupport from the project because it's using Swift Package Manager to pull from here. I'm using Deferred version 3.0.0

[zwaldowski]

I'm afraid this has to do with the following:

• https://bugs.swift.org/browse/SR-3034
• [sil-dead-function-elimination] Do not remove bodies of transparent functions referenced from vtables and witness tables swiftlang/swift#6428
• Make SwiftPM testable in release mode swiftlang/swift-package-manager#758

Some strategies I can think of:

• Update your buildpack to Swift 3.0.1 or 3.1.
• If you can control the SwiftPM command-line arguments, try adding -Xswiftc -enable-testing.
• If you simply cannot mitigate any other way, remove Deferred's tests and their entries in the Package.swift file.

I'm sorry for the inconvenience. I'm not sure there's much we can do on our end to mitigate this problem.