message: Fix check for 64 bit on Windows relying on MSVC
diff: @@ -226,7 +226,7 @@ elseif(WIN32)
  set(CPACK_NSIS_EXECUTABLES_DIRECTORY ".")
  set(CPACK_NSIS_MUI_FINISHPAGE_RUN ${GITTYUP_NAME}.exe)
  - if(CMAKE_CL_64)
  + if(CMAKE_SIZEOF_VOID_P EQUAL 8)
  install(
  FILES ${RSRC_DIR}/vcredist_x64.exe
  DESTINATION .
  