mingw: use modern strftime implementation if possible

[rimrul]

Microsoft introduced a new "Universal C Runtime Library" (UCRT) with
Visual Studio 2015. The UCRT comes with a new strftime() implementation that
supports more date formats. We link git against the older "Microsoft Visual C
Runtime Library" (MSVCRT), so to use the UCRT strftime() we need to load it from
ucrtbase.dll using DECLARE_PROC_ADDR()/INIT_PROC_ADDR().

Most supported Windows systems should have recieved the UCRT via Windows update,
but in some cases only MSVCRT might be available. In that case we fall back to
using that implementation.

[rimrul]

Looking back at the diff, it might make sense to move _fallback_strftime and it's initialization into mingw_strftime().

[dscho]

In addition to moving it inside, can we also initialize it directly, i.e. static int (*fallback)(...) = strftime;?

[rimrul]

static int

Microsoft says it should be size_t, not int
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strftime-wcsftime-strftime-l-wcsftime-l?view=vs-2019

(*fallback)(...) = strftime;

yeah, I guess that works. I'll prepare an updated version.

[dscho]

Sorry, on my phone, couldn't cut 'n paste.

[dscho]

Perfect, @rimrul you're awesome!

[TheStormN]

@dscho @rimrul
Sorry to bring this back, I saw it from the new version changelog, The current code doesn't seem very optimal. Why try to load and resolve the address of strftime every time? Just do it once per startup and use the pointer.

This might not seem like a big deal for programs that use strftime rarely but because it is inside the mingw implementation I think it needs to be more optimal.

[rimrul]

That's exactly what we do. INIT_PROC_ADDR caches the address.

See it's implementation here: https://github.com/git/git/blob/53f9a3e157dbbc901a02ac2c73346d375e24978c/compat/win32/lazyload.h#L31-L55

[TheStormN]

Oh, ok, thank you for the clarification and sorry for the misunderstanding. :)