Xcode - XCConfig conditional causing illegal instruction 4

I have a project that I recently upgraded to Xcode 10 Beta 5, however, using the CLI xcodebuild now gives me this error:

"Illegal instruction: 4"

Some troubleshooting determined that the xcconfig file specified in the xcodebuild command causes the problem, specifically the conditional e.g. [sdk=iphoneos*].

Omitting this conditional allows the build to run fine. It runs fine within Xcode as well. However, we need the CLI to work.

Reproducible steps:

1. Create an empty Xcode Project
2. Create an xcconfig for its target
3. Add a line e.g. CODE_SIGN_IDENTITY[sdk=iphoneos*] = iPhone Developer
4. Attempt to build from CLI specifying the xcconfig file. (It will fail)
5. Change the line to CODE_SIGN_IDENTITY = iPhone Developer . Build will work.