Unguarded use of `nl_langinfo` on `_Py_GetLocaleEncoding`

[AGraber]

Bug report

Bug description:

When building on a platform that is not Windows and HAVE_LANGINFO_H is not defined, building can fail because _Py_GetLocaleEncoding attempts to use nl_langinfo regardless:

cpython/Python/fileutils.c

Lines 906 to 918 in 7241f27

	#ifdef MS_WINDOWS
	wchar_t encoding[23];
	unsigned int ansi_codepage = GetACP();
	swprintf(encoding, Py_ARRAY_LENGTH(encoding), L"cp%u", ansi_codepage);
	encoding[Py_ARRAY_LENGTH(encoding) - 1] = 0;
	return _PyMem_RawWcsdup(encoding);
	#else
	const char *encoding = nl_langinfo(CODESET);
	if (!encoding || encoding[0] == '\0') {
	// Use UTF-8 if nl_langinfo() returns an empty string. It can happen on
	// macOS if the LC_CTYPE locale is not supported.
	return _PyMem_RawWcsdup(L"utf-8");
	}

Maybe if there's no other way to tell it can just default to UTF-8 like Android or etc.

CPython versions tested on:

3.14

Operating systems tested on:

Other

[StanFromIreland]

It doesn’t fail on Android because it defines _Py_FORCE_UTF8_LOCALE:

cpython/Include/pyport.h

Lines 505 to 509 in 7241f27

	#if defined(__ANDROID__) || defined(__VXWORKS__)
	// Use UTF-8 as the locale encoding, ignore the LC_CTYPE locale.
	// See _Py_GetLocaleEncoding(), PyUnicode_DecodeLocale()
	// and PyUnicode_EncodeLocale().
	# define _Py_FORCE_UTF8_LOCALE