Fix -Wformat / -Wformat-non-iso on MinGW UCRT

[tongyuantongyu]

MinGW can be configured to use UCRT, which is the new C runtime library for Windows. I'm moving my MinGW dev environment to the UCRT variant.

UCRT supports "%zu" properly so MinGW didn't patch*printf functions and set __USE_MINGW_ANSI_STDIO to 1. This makes AVIF_FMT_ZU defined to "%Iu", and triggers warning from GCC and Clang.

Detect UCRT by check _UCRT macro, which MSSVC and MinGW both defines, and use "%zu" when using UCRT.

[y-guyon]

Is it possible to use UCRT with Visual Studio before 2013? Otherwise it can be "simplified" to:

#if (defined(_MSVC) && _MSVC < 1800) || (defined(__USE_MINGW_ANSI_STDIO) && __USE_MINGW_ANSI_STDIO == 0 && !defined(_UCRT))

[tongyuantongyu]

VS <= 2013 never use UCRT and VS >= 2015 always use UCRT.
However, I find this expression easier to understand:

we want a feature in the C runtime.

• UCRT definitely provides it.
• msvcr120 (the version of msvcrt Visual Studio 2013 uses) provides it, but no macro can be used to test CRT version so test Visual Studio version instead.
• MinGW sometimes provides it by patch and we can test if the patch is applied.

[wantehchang]

Hi Yuan,

It is reasonable to require Visual Studio 2015 or later today. For example, libaom requires Visual Studio 2017 or later:

https://aomedia.googlesource.com/aom/+/master/README.md#microsoft-visual-studio-builds

Let's drop support for Visual Studio 2013 or older. Could you simplify this expression?

[tongyuantongyu]

Done

[kmilos]

Actually, this is much better/cleaner fixed by using standard PRI* print formatters from inttypes.h directly in libavif instead of trying to figure it out here.

inttypes.h under MinGW implementation already does the correct #if defined(_UCRT) || __USE_MINGW_ANSI_STDIO for you.

Edit: scratch that, sorry... I now see inttypes.h doesn't define a format for size_t, so this is ok... unless you want to use PRIuPTR (uintptr_t is the same or wider than size_t).

[wantehchang]

LGTM. I edited the comment slightly.

[wantehchang]

@tongyuantongyu Yuan: I added "if" after "even". I am less certain about this change. Please check it. Thanks.