Link external libs in global_communication test (#133)

* Add `target_link_libraries` for external libs in `tests/global_communication/CMakeLists.txt`.

Fixes issue #132

tests/global_communication/CMakeLists.txt

@@ -16,10 +16,7 @@ set(TARGETS global_communication.exe)
 
 foreach(target ${TARGETS})
     target_link_libraries(${target} LINK_PUBLIC nestmc gtest)
-
-    if(WITH_TBB)
-        target_link_libraries(${target} LINK_PUBLIC ${TBB_LIBRARIES})
-    endif()
+    target_link_libraries(${target} LINK_PUBLIC ${EXTERNAL_LIBRARIES})
 
     if(WITH_MPI)
         target_link_libraries(${target} LINK_PUBLIC ${MPI_C_LIBRARIES})