gh-131942: Use the Python-specific Py_DEBUG macro rather than _DEBUG in Windows-related C code

[XuehaiPan]

Changes:

1. Move the definition of Py_DEBUG in PC/pyconfig.h.in to the top of the file.

/* _DEBUG implies Py_DEBUG */#ifdef_DEBUG#definePy_DEBUG#endif

2. Change usage of _DEBUG to Py_DEBUG by using the regex /\b_DEBUG\b/.
3. Update the generated files via make regen-all.

---

Since the sysconfig.h is included in all C headers with top precedence. This PR does not have any user-side visible changes.

cpython/Include/Python.h

Lines 5 to 15 in 4940d96

	#ifndefPy_PYTHON_H
	#definePy_PYTHON_H
	// Since this is a "meta-include" file, "#ifdef __cplusplus / extern "C" {"
	// is not needed.
	// Include Python header files
	#include"patchlevel.h"
	#include"pyconfig.h"
	#include"pymacconfig.h"

Resolves#131942

• Issue: Use the Python-specific Py_DEBUG macro rather than _DEBUG in Windows-related C code #131942

[vstinner]

cc @zooba@zware

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[zooba]

Updating the documentation isn't required, but if you're going to, we should document the Windows behaviour on the same level as the Unix behaviour (that is, don't put it in a "note"), and should also make the whole section make sense.

[zooba]

Apologies for the delays, and thanks for the updates.

Once CI passes, this will merge automatically. Thanks!