Update usages of `PySys_FormatStderr` with locale-dependent `strerror`

[picnixz]

strerror is locale-dependent but PySys_FormatStderr is not. The usage is

cpython/Modules/main.c

Lines 377 to 379 in 7303f06

	// TODO(picnixz): strerror() is locale dependent but not PySys_FormatStderr().
	PySys_FormatStderr("%S: can't open file %R: [Errno %d] %s\n",
	program_name, filename, errno, strerror(errno));

and we should update it to be locale-dependent. This is a follow-up to #126746 (comment).

This would be quite hard to test as pointed out by Serhiy, so I won't work on this for now. Others may pick that task.

[vstinner]

There is a simple fix: remove strerrror().

[vstinner]

At this point, the LC_MESSAGES locale is still the default C locale, the error message is not localized, and so is very likely an English message which is ASCII friendly.

Maybe the exception would be if Python is embedded and Py_Main() (or any other function to embed Python) is called with LC_MESSAGES configured to something else.

[picnixz]

At this point, the LC_MESSAGES locale is still the default C locale, the error message is not localized, and so is very likely an English message which is ASCII friendly.

Oh! I thought it was already localized. So maybe it's a non-issue? I didn't investigate more in details since I'm not well-versed in embedded Python, hence the TODO I left. But if it's a non-issue, we can try:

• try to use strerror() normally -> hopefully nothing fails
• if we have some UnicodeDecodeError -> clear it and remove strerror()
• format a new exception without the use of strerror() now.

If it's too much for something that is too rare, I think we should remove the "TODO(picnixz)" message (I can remove it as part of #128025 if the latter is not merged yet).