COMP: Support packaging in Slicer custom app

This commit refactors the install rules introducing EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS variable expected by the Slicer build system to bundle "Superbuild" based extension.

Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

CMakeLists.txt

@@ -54,9 +54,11 @@ include(${Slicer_EXTENSION_GENERATE_CONFIG})
 
 #-----------------------------------------------------------------------------
 # Packaging
-set(CPACK_INSTALL_CMAKE_PROJECTS "${CPACK_INSTALL_CMAKE_PROJECTS};${CMAKE_BINARY_DIR};${EXTENSION_NAME};ALL;/")
-set(CPACK_INSTALL_CMAKE_PROJECTS "${CPACK_INSTALL_CMAKE_PROJECTS};${OpenIGTLink_DIR};OpenIGTLink;RuntimeLibraries;/")
-set(CPACK_INSTALL_CMAKE_PROJECTS "${CPACK_INSTALL_CMAKE_PROJECTS};${OpenIGTLinkIO_DIR};OpenIGTLinkIO;RuntimeLibraries;/")
+set(EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS)
+list(APPEND EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS "${OpenIGTLink_DIR};OpenIGTLink;RuntimeLibraries;/")
+list(APPEND EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS "${OpenIGTLinkIO_DIR};OpenIGTLinkIO;RuntimeLibraries;/")
+set(${EXTENSION_NAME}_CPACK_INSTALL_CMAKE_PROJECTS "${EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS}" CACHE STRING "List of external projects to install" FORCE)
+list(APPEND CPACK_INSTALL_CMAKE_PROJECTS "${CMAKE_BINARY_DIR};${EXTENSION_NAME};ALL;/")
+list(APPEND CPACK_INSTALL_CMAKE_PROJECTS "${${EXTENSION_NAME}_CPACK_INSTALL_CMAKE_PROJECTS}")
 include(${CMAKE_CURRENT_SOURCE_DIR}/CMake/SlicerBlockInstallVP9.cmake)
-message(STATUS "CPACK_INSTALL_CMAKE_PROJECTS = ${CPACK_INSTALL_CMAKE_PROJECTS}")
 include(${Slicer_EXTENSION_CPACK})