Correctly casting toolchain features to a set.

Before, the get_config function was checking the equality of a set and a
list. However the list's equality depends on order, so this change casts
it to set to prevent an infinite loop.

tools/build_api.py

@@ -134,7 +134,7 @@ def get_config(src_paths, target, toolchain_name):
         toolchain.config.add_config_files(resources.json_files)
 
         # Add features while we find new ones
-        features = toolchain.config.get_features()
+        features = set(toolchain.config.get_features())
         if features == prev_features:
             break