empty list of libraries to link with a target causes gersemi crash

[michalkaptur]

description

Although technically empty list of libraries to link with a target makes no sense, it's apparently a legal cmake syntax.
gersemi should not crash.

version

gersemi 0.9.4
lark 1.1.8
Python 3.9.18 (main, Oct 24 2023, 14:13:49) 

how to reproduce

$ cat CMakeLists.txt
target_link_libraries(foo)
$ gersemi CMakeLists.txt

outcome

multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 48, in mapstar
    return list(map(*args))
  File "/tmp/.venv/lib/python3.9/site-packages/gersemi/runner.py", line 126, in run_task
    to_stderr=get_error_message(formatted_file),
  File "/tmp/.venv/lib/python3.9/site-packages/gersemi/result.py", line 36, in get_error_message
    exception, path = astuple(error)
  File "/usr/lib/python3.9/dataclasses.py", line 1140, in astuple
    return _astuple_inner(obj, tuple_factory)
  File "/usr/lib/python3.9/dataclasses.py", line 1147, in _astuple_inner
    value = _astuple_inner(getattr(obj, f.name), tuple_factory)
  File "/usr/lib/python3.9/dataclasses.py", line 1167, in _astuple_inner
    return copy.deepcopy(obj)
  File "/usr/lib/python3.9/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib/python3.9/copy.py", line 264, in _reconstruct
    y = func(*args)
TypeError: __init__() missing 2 required positional arguments: 'obj' and 'orig_exc'
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/tmp/.venv/bin/gersemi", line 8, in <module>
    sys.exit(main())
  File "/tmp/.venv/lib/python3.9/site-packages/gersemi/__main__.py", line 173, in main
    sys.exit(run(mode, configuration, args.sources))
  File "/tmp/.venv/lib/python3.9/site-packages/gersemi/runner.py", line 189, in run
    results = [
  File "/tmp/.venv/lib/python3.9/site-packages/gersemi/runner.py", line 189, in <listcomp>
    results = [
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 448, in <genexpr>
    return (item for chunk in result for item in chunk)
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 870, in next
    raise value
TypeError: __init__() missing 2 required positional arguments: 'obj' and 'orig_exc'