Fix Slicer extension build on windows

[jcfr]

 exit /b %1
    :cmDone
    if %errorlevel% neq 0 goto :VCEnd
    :VCEnd
    -- Install configuration: "Release"
    CMake Error at cmake_install.cmake:36 (file):
      file INSTALL cannot find
      "D:/D/P/Slicer-481-package/Slicer-build/lib/Slicer-4.8/cli-modules/Debug/polydatatransform.exe".

See http://slicer.cdash.org/viewBuildError.php?buildid=1368063