Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.

Problem:    Code is indented more than necessary.
Solution:   Use an early return where it makes sense. (Yegappan Lakshmanan,
            closes #11805)

Problem:    Complicated use of #ifdef.
Solution:   Simplify #ifdef use. (Ken Takata, closes #11745)

Problem:    Preprocessor indenting is off.
Solution:   Adjust preprocessor indentation. (Ken Takata, closes #11546)

Problem:    Deprecation warning causes build failure.
Solution:   Suppress deprecation warning. (closes #11503)

Problem:    Compiler warning for redefining HAVE_DUP.
Solution:   Undefine HAVE_DUP if needed. (Ozaki Kiichi, closes #11484)

Problem:    Cannot build with Python 3.11.
Solution:   Adjust define for _PyObject_TypeCheck. (Zdenek Dohnal,
            closes #10627)

Problem:    MS-Windows: Vim exits when Python 3 initialisation fails.
Solution:   Hook into the exit() function to recover from the failure.
            (Ken Takata, closes #9710)

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.