Modules/Platform/iOS-Initialize.cmake - third_party/github.com/Kitware/CMake - Git at Google

 include(Platform/Darwin-Initialize)

 if(NOT _CMAKE_OSX_SYSROOT_PATH MATCHES "/(iPhoneOS|iPhoneSimulator|MacOSX)")
   message(FATAL_ERROR "${CMAKE_OSX_SYSROOT} is not an iOS SDK")
 endif()

 set(IOS 1)
	include(Platform/Darwin-Initialize)

	if(NOT _CMAKE_OSX_SYSROOT_PATH MATCHES "/(iPhoneOS\|iPhoneSimulator\|MacOSX)")
	message(FATAL_ERROR "${CMAKE_OSX_SYSROOT} is not an iOS SDK")
	endif()

	set(IOS 1)