Specify the location or name of the macOS 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 should be set as a
CACHE entry (or else CMake may
remove it while initializing a cache entry of the same name).
OSX part in the variable name(s) they apply also to
other SDKs than macOS like iOS, tvOS, or watchOS.
This variable is ignored on platforms other than Apple.