cmake: make Lts subdirs MIGRATE_MODULE-guarded (use NGL_ADD_SUBDIR_GUARDED)

Lts/CMakeLists.txt

@@ -19,10 +19,11 @@ endif()
 set(LTS_SUBDIRS Tools Application Common DDS Plugins Projects Proxies Services Viewer)
 foreach(dir IN LISTS LTS_SUBDIRS)
   if (EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/${dir}")
-    ADD_SUBDIRECTORY(${dir})
-  else()
-    message(STATUS "Skipping missing Lts subdirectory: ${dir}")
-  endif()
+  # Use guarded add so top-level MIGRATE_MODULE can restrict which Lts subdirs are included
+  NGL_ADD_SUBDIR_GUARDED(${dir})
+else()
+  message(STATUS "Skipping missing Lts subdirectory: ${dir}")
+endif()
 
 endforeach()