Specify the location or name of the OS X platform SDK to be used.
CMake uses this value to compute the value of the
or equivalent and to help the
find_* commands locate files in
If not set explicitly the value is initialized by the
environment variable, if set, and otherwise computed based on the
CMAKE_OSX_DEPLOYMENT_TARGET or the host platform.
The value of this variable should be set prior to the first
enable_language() command invocation
because it may influence configuration of the toolchain and flags.
It is intended to be set locally by the user creating a build tree.
This variable is ignored on platforms other than OS X.