Kitware/CMake — pull request #23 by jdicioccio (2012-08-07 23:17:50+00:00)
Title: Add CMAKE_OSX_SDKSTRING to set SDKROOT string in pbxproj file

The existing SDKROOT variable is insufficient, because it is
required that it be a path. However, there are additional
valid values for SDKROOT in the pbxproj, such as "iphoneos"

This variable allows the use of these magic strings