ui/cold-revng needs ui/qt-creator sources

Sadly, QtCreator plugins need includes from QtCreator source code.  In
future, we'll need to be able to express dependencies on the source code
of other components. For now, just invoke `orc clone ui/qt-creator`.

.orchestra/config/components/ui/cold_revng.yml

@@ -5,6 +5,8 @@
 
 ---
 #@ def build_args():
+pre_configure_script: |
+  orc clone --no-force ui/qt-creator
 extra_cmake_args:
   - #@ template.replace(cmake_boost_configuration)
   #! TODO: this is really ugly hack to get the same value of QTC_SOURCE as legacy orchestra