build: properly propagate included directories from dependencies

build-support/custom-modules/ns3-module-macros.cmake

@@ -193,6 +193,20 @@ function(build_lib)
     ${lib${BLIB_LIBNAME}} ${exported_libraries} ${private_libraries}
   )
 
+  if(NOT ${XCODE})
+    # Since linking libraries to object libraries in not allowed in older CMake
+    # releases, we need to import each of their include directories. Otherwise,
+    # include directories won't be properly propagated
+    set(temp)
+    foreach(target ${ns_libraries_to_link})
+      list(APPEND temp
+           "$<TARGET_PROPERTY:${target},INTERFACE_INCLUDE_DIRECTORIES>"
+      )
+    endforeach()
+    target_include_directories(${lib${BLIB_LIBNAME}}-obj PRIVATE ${temp})
+    unset(temp)
+  endif()
+
   # set output name of library
   set_target_properties(
     ${lib${BLIB_LIBNAME}}