Fix windows.


git-svn-id: https://root.cern.ch/svn/root/trunk@48319 27541ba8-7e3a-0410-8455-c3a389f83636
In our buildsystem nobody defines HAVE_UNISTD_H yet.


git-svn-id: https://root.cern.ch/svn/root/trunk@48320 27541ba8-7e3a-0410-8455-c3a389f83636