Fix path to icons (XXX)

Index: release/scripts/startup/bl_ui/space_toolsystem_common.py
--- release/scripts/startup/bl_ui/space_toolsystem_common.py.orig
+++ release/scripts/startup/bl_ui/space_toolsystem_common.py
@@ -235,8 +235,8 @@ class ToolSelectPanelHelper:
             assert(type(icon_name) is str)
             icon_value = _icon_cache.get(icon_name)
             if icon_value is None:
-                dirname = bpy.utils.system_resource('DATAFILES', path="icons")
-                filename = os.path.join(dirname, icon_name + ".dat")
+                dirname = os.environ['BLENDER_SYSTEM_DATAFILES']
+                filename = os.path.join(dirname, "icons", icon_name + ".dat")
                 try:
                     icon_value = bpy.app.icons.new_triangles_from_file(filename)
                 except Exception as ex:
