Tests: Teach RunCMake to ignore Xcode DVTCoreDeviceEnabledState warnings

On some Xcode versions, `xcodebuild` may warn:

    ... xcodebuild[...] DVTCoreDeviceEnabledState: DVTCoreDeviceEnabledState_Disabled set via user default

Teach RunCMake to drop such incidental lines before matching against
expected output.