I still think that the includedir and sysincludedir usage in the Xcode project is still up for debate on the correct behaviour, but I think restoring the previous functionality first and then carefully revisiting the specs later before making any major decisions.
Based on our discussions https://github.com/premake/premake-xcode/pull/26, I'm requesting the revert of merge #26 as it lost an important unit test and caused a spacing bug in the process.
I still think that the includedir and sysincludedir usage in the Xcode project is still up for debate on the correct behaviour, but I think restoring the previous functionality first and then carefully revisiting the specs later before making any major decisions.