Problem:
- `gen_str_catalog.py` uses `libclang` to parse enumeration data.

Solution:
- Install `libclang`.

Problem:
- If `libclang` is not available for `gen_str_catalog.py`, it is possible to
  provide (by fixed manual input) the `enums` part of the JSON output. When
  `libclang` is available, this input would be discarded -- regardless of
  whether it contains enum keys which aren't from parsing.

Solution:
- Merge the dictionaries for the parsed enum values.