Returns the Xcode build version. This is an alphanumeric string as output by xcodebuild -version and shown in the About Xcode window. This value is embedded into the
plist of app bundles built by Xcode, under the field named DTXcodeBuild
developerDir - Path to developer dir, i.e. /Applications/Xcode.app/Contents/Developer
the xcode build version if found, nothing if it fails to be found, or the version
plist file cannot be read.