In C, a narrow type is automatically extended, so those verbose suffixes
are not needed for anything.

Only whitespace changes.

[5/10] Compiling C object src/systemd/login.cpython-313-x86_64-linux-gnu.so.p/login.c.o
../src/systemd/login.c:321:1: warning: missing initializer for field ‘m_slots’ of ‘struct PyModuleDef’ [-Wmissing-field-initializers]
  321 | };
      | ^
In file included from /usr/include/python3.13/Python.h:95,
                 from ../src/systemd/login.c:6:
/usr/include/python3.13/moduleobject.h:113:21: note: ‘m_slots’ declared here
  113 |   PyModuleDef_Slot *m_slots;
      |                     ^~~~~~~

[6/18] Compiling C object src/systemd/_daemon.cpython-313-x86_64-linux-gnu.so.p/_daemon.c.o
../src/systemd/_daemon.c:415:37: warning: cast between incompatible function types from ‘PyObject * (*)(PyObject *, PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *, struct _object *)’} to ‘PyObject * (*)(PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *)’} [-Wcast-function-type]
  415 |         { "notify",                 (PyCFunction) notify,     METH_VARARGS | METH_KEYWORDS, notify__doc__                },
      |                                     ^
../src/systemd/_daemon.c:416:37: warning: cast between incompatible function types from ‘PyObject * (*)(PyObject *, PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *, struct _object *)’} to ‘PyObject * (*)(PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *)’} [-Wcast-function-type]
  416 |         { "_listen_fds",            (PyCFunction) listen_fds, METH_VARARGS | METH_KEYWORDS, listen_fds__doc__            },
      |                                     ^
../src/systemd/_daemon.c:417:37: warning: cast between incompatible function types from ‘PyObject * (*)(PyObject *, PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *, struct _object *)’} to ‘PyObject * (*)(PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _object *, struct _object *)’} [-Wcast-function-type]
  417 |         { "_listen_fds_with_names", (PyCFunction) listen_fds_with_names,
      |                                     ^

This is a problem in the Python C API… They should have used a union type.

One-letter name is fine for a local variable, but it seems iffy to name
a structure field like this.

Since Python 3.0 it is an alias for OSError.

They were a 1:1 mapping anyway.

We're not going to be compiling any other C code, so let's simplify
this.

systemd headers should be included using <>.
And use a single include of Python.h and define PY_SSIZE_T_CLEAN
before it, so that we're using a consistent API everywhere.