Fixed outdated builds on VS2012
Fixed outdated builds on VS2012

High-level build did not build external projects in VS2012.
The BUILD_ALWAYS flag is a relatively new CMake feature (added in 3.1),
therefore the following workaround was added into SuperBuild.cmake:

ExternalProject_Add_Step(${proj} forcebuild
  COMMAND ${CMAKE_COMMAND} -E remove
    ${CMAKE_CURRENT_BINARY_DIR}/${proj}-prefix/src/${proj}-stamp/${proj}-build
  COMMENT "Forcing build step for '${proj}'"
  DEPENDEES build
  ALWAYS 1
  )

This does not work with Visual Studio, where the stamp file is in Debug/Release/etc. subdirectory:
${CMAKE_CURRENT_BINARY_DIR}/${proj}-prefix/src/${proj}-stamp/${CMAKE_CFG_INTDIR}/${proj}CTK-build

Co-authored-by: Jean-Christophe Fillion-Robin <859d3fd8ca46de62a08fca56c64958e301f5352c@kitware.com>

CJGoch/CTK,SINTEFMedtek/CTK,AndreasFetzer/CTK,SINTEFMedtek/CTK,sankhesh/CTK,mehrtash/CTK,sankhesh/CTK,ddao/CTK,jcfr/CTK,151706061/CTK,151706061/CTK,rkhlebnikov/CTK,msmolens/CTK,SINTEFMedtek/CTK,jcfr/CTK,fedorov/CTK,fedorov/CTK,Sardge/CTK,rkhlebnikov/CTK,CJGoch/CTK,naucoin/CTK,151706061/CTK,AndreasFetzer/CTK,rkhlebnikov/CTK,AndreasFetzer/CTK,Heather/CTK,Sardge/CTK,commontk/CTK,msmolens/CTK,jcfr/CTK,Heather/CTK,Sardge/CTK,sankhesh/CTK,naucoin/CTK,ddao/CTK,naucoin/CTK,mehrtash/CTK,ddao/CTK,commontk/CTK,ddao/CTK,msmolens/CTK,Heather/CTK,Sardge/CTK,fedorov/CTK,151706061/CTK,jcfr/CTK,naucoin/CTK,sankhesh/CTK,SINTEFMedtek/CTK,CJGoch/CTK,jcfr/CTK,fedorov/CTK,AndreasFetzer/CTK,msmolens/CTK,rkhlebnikov/CTK,commontk/CTK,Heather/CTK,mehrtash/CTK,CJGoch/CTK,CJGoch/CTK,151706061/CTK,commontk/CTK,SINTEFMedtek/CTK,mehrtash/CTK