Currently the CMAKE_XCODE_EFFECTIVE_PLATFORMS property acts only as
a kind of toggle switch to enable iOS project layout features.
But instead of relying on this undocumented property, better detect
the presence of an iOS SDK directly.
Presently, this test is only run manually because not all machines
have an iOS SDK, complications associated with certificates and code
signing, having a device attached, ...
If you're setup to do iOS dev work, you can easily run this test
manually on your Mac using the Xcode generator and run the result
in the simulator or on your attached device.