COMP: correct innerbuild list separator

CMake/External/CMakeLists.txt

@@ -147,6 +147,7 @@ ExternalProject_Add( ${PROJECT_NAME}
   SOURCE_DIR ${${PROJECT_NAME}_SOURCE_DIR}
   BINARY_DIR ${CMAKE_BINARY_DIR}/Innerbuild
   CMAKE_GENERATOR ${CMAKE_GENERATOR}
+  LIST_SEPARATOR ${_sep_}
   CMAKE_ARGS
     -D${PROJECT_NAME}_SUPERBUILD:BOOL=OFF
     ${CMAKE_CONFIG_ARGS}