[build tools] Added support for completely overriding cumulative attributes

Author: geky

tools/config.py

@@ -226,6 +226,11 @@ def _process_config_and_overrides(self, data, params, unit_name, unit_kind):
                 for attr in Target._Target__cumulative_attributes:
                     attrs = getattr(self.target_instance, attr)
 
+                    if attr in overrides:
+                        del attrs[:]
+                        attrs.extend(overrides[attr])
+                        del overrides[attr]
+
                     if attr+'_add' in overrides:
                         attrs.extend(overrides[attr+'_add'])
                         del overrides[attr+'_add']