CMAKE_OSX_SYSROOT

Specify the location or name of the OS X platform SDK to be used. CMake uses this value to compute the value of the -isysroot flag or equivalent and to help the find_* commands locate files in the SDK.

If not set explicitly the value is initialized by the SDKROOT 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 project() or 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.

Despite the 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.