Restore KWSys SystemTools _WIN32 state on cygwin
Restore KWSys SystemTools _WIN32 state on cygwin

The commit "Fix KWSys SystemTools build on cygwin with -mwin32" tried to
restore the state of the _WIN32 definition that was broken by the commit
"Optimize KWSys SystemTools::FileExists on Windows".  It did so for the
case of building with -mwin32 on cygwin, but since including <windows.h>
defines _WIN32, it failed for the case of not using -mwin32.

This commit restores the state of _WIN32 in all cases by undefining it
after including <windows.h> if it was not defined beforehand.

Wuteyan/VTK,collects/VTK,jeffbaumes/jeffbaumes-vtk,msmolens/VTK,mspark93/VTK,Wuteyan/VTK,gram526/VTK,cjh1/VTK,arnaudgelas/VTK,aashish24/VTK-old,naucoin/VTKSlicerWidgets,daviddoria/PointGraphsPhase1,Wuteyan/VTK,hendradarwin/VTK,sumedhasingla/VTK,gram526/VTK,arnaudgelas/VTK,gram526/VTK,candy7393/VTK,biddisco/VTK,jeffbaumes/jeffbaumes-vtk,sankhesh/VTK,jmerkow/VTK,msmolens/VTK,demarle/VTK,candy7393/VTK,berendkleinhaneveld/VTK,aashish24/VTK-old,keithroe/vtkoptix,johnkit/vtk-dev,hendradarwin/VTK,sumedhasingla/VTK,berendkleinhaneveld/VTK,daviddoria/PointGraphsPhase1,sumedhasingla/VTK,ashray/VTK-EVM,msmolens/VTK,SimVascular/VTK,biddisco/VTK,sumedhasingla/VTK,Wuteyan/VTK,cjh1/VTK,jeffbaumes/jeffbaumes-vtk,biddisco/VTK,demarle/VTK,gram526/VTK,sankhesh/VTK,sankhesh/VTK,sankhesh/VTK,mspark93/VTK,hendradarwin/VTK,ashray/VTK-EVM,collects/VTK,Wuteyan/VTK,keithroe/vtkoptix,candy7393/VTK,keithroe/vtkoptix,daviddoria/PointGraphsPhase1,jmerkow/VTK,SimVascular/VTK,demarle/VTK,collects/VTK,Wuteyan/VTK,demarle/VTK,spthaolt/VTK,arnaudgelas/VTK,jmerkow/VTK,jmerkow/VTK,mspark93/VTK,keithroe/vtkoptix,spthaolt/VTK,ashray/VTK-EVM,spthaolt/VTK,naucoin/VTKSlicerWidgets,aashish24/VTK-old,jmerkow/VTK,candy7393/VTK,johnkit/vtk-dev,collects/VTK,keithroe/vtkoptix,sankhesh/VTK,berendkleinhaneveld/VTK,keithroe/vtkoptix,candy7393/VTK,daviddoria/PointGraphsPhase1,aashish24/VTK-old,hendradarwin/VTK,mspark93/VTK,aashish24/VTK-old,berendkleinhaneveld/VTK,daviddoria/PointGraphsPhase1,sankhesh/VTK,gram526/VTK,demarle/VTK,johnkit/vtk-dev,biddisco/VTK,collects/VTK,gram526/VTK,keithroe/vtkoptix,hendradarwin/VTK,candy7393/VTK,spthaolt/VTK,berendkleinhaneveld/VTK,johnkit/vtk-dev,jmerkow/VTK,SimVascular/VTK,biddisco/VTK,spthaolt/VTK,spthaolt/VTK,hendradarwin/VTK,johnkit/vtk-dev,cjh1/VTK,ashray/VTK-EVM,johnkit/vtk-dev,sumedhasingla/VTK,sumedhasingla/VTK,cjh1/VTK,jeffbaumes/jeffbaumes-vtk,biddisco/VTK,berendkleinhaneveld/VTK,gram526/VTK,mspark93/VTK,naucoin/VTKSlicerWidgets,collects/VTK,cjh1/VTK,msmolens/VTK,daviddoria/PointGraphsPhase1,msmolens/VTK,mspark93/VTK,sankhesh/VTK,naucoin/VTKSlicerWidgets,SimVascular/VTK,demarle/VTK,SimVascular/VTK,spthaolt/VTK,biddisco/VTK,SimVascular/VTK,gram526/VTK,ashray/VTK-EVM,mspark93/VTK,Wuteyan/VTK,keithroe/vtkoptix,msmolens/VTK,demarle/VTK,SimVascular/VTK,jeffbaumes/jeffbaumes-vtk,naucoin/VTKSlicerWidgets,johnkit/vtk-dev,candy7393/VTK,naucoin/VTKSlicerWidgets,jmerkow/VTK,msmolens/VTK,SimVascular/VTK,ashray/VTK-EVM,aashish24/VTK-old,berendkleinhaneveld/VTK,cjh1/VTK,sumedhasingla/VTK,msmolens/VTK,arnaudgelas/VTK,ashray/VTK-EVM,ashray/VTK-EVM,arnaudgelas/VTK,demarle/VTK,jmerkow/VTK,sumedhasingla/VTK,jeffbaumes/jeffbaumes-vtk,mspark93/VTK,arnaudgelas/VTK,candy7393/VTK,hendradarwin/VTK,sankhesh/VTK