Fix function macros with empty params list

[mara004]

This fixes a bug in compiling function macros without params that was present in ctypesgen since at least 2008 according to git blame.

Previously, e.g. the following macro from pymacro.h

#  define Py_UNREACHABLE() \
    Py_FatalError("Unreachable C code path reached")

would translate to

Py_UNREACHABLE = Py_FatalError("Unreachable C code path reached")

which (without try/except guards) promptly raises an exception when importing the module, rendering the macro unusable.
i.e. macros without params were not translated to a function, but the action was called once on import time, and the symbol name merely got assigned the return value of that call.

With this patch, it now correctly translates to

def Py_UNREACHABLE():
    return Py_FatalError('Unreachable C code path reached')

---

This was discovered during development of the pypdfium2-team fork, thanks to a new option to disable macro guards.
I thought I'd also submit it here because it's a very simple, standalone fix.

[nilason]

There is a flake8 failure, please correct it.

[mara004]

There is a flake8 failure, please correct it.

Due to line length I think. I don't usually hard wrap lines and rely on dynamic viewer wrapping instead.
Feel free to update the PR using GH CLI.

I'm mostly working with my own, revised codebase now, and am not interested in flake compliance. Feel free to pick what you like, while I try to submit simple patches or give pointers here as well. But I don't intend to spend time on the usual PR process any longer.

[mara004]

Thanks!