Add sprintf, snprintf, and the scanf family for Windows

[dropbear32]

Description

This adds declarations for the following functions for Windows:

• sprintf
• snprintf
• scanf
• sscanf
• fscanf

As noted in #2860, these are provided by legacy_stdio_definitions.lib in newer versions of Windows, so they're behind the same gate.

This fixes #4995.

Sources

• https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/sprintf-sprintf-l-swprintf-swprintf-l-swprintf-l
• https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/snprintf-snprintf-snprintf-l-snwprintf-snwprintf-l
• https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/scanf-scanf-l-wscanf-wscanf-l
• https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/sscanf-sscanf-l-swscanf-swscanf-l
• https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fscanf-fscanf-l-fwscanf-fwscanf-l

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget); especially relevant for platforms that may not be checked in CI

@rustbot label +stable-nominated

[tgross35]

The definitions look fine, but what is the story with legacy_stdio_definitions? I don't know if there's a reason users should be avoiding symbols that aren't in the ucrt, though I don't really understand why these wouldn't be in the ucrt in the first place.

Cc @ChrisDenton for thoughts here.

[dropbear32]

For whatever reason, Microsoft moved to defining these inline in stdio.h: https://learn.microsoft.com/en-us/cpp/porting/visual-cpp-change-history-2003-2015#stdio_and_conio

They provide legacy_stdio_definitions.lib as a compatibility measure if you're not using the header that defines these functions.

[ChrisDenton]

Yep, they're defined inline. We could potentially write our own wrappers around the internal versions but I've not investigated that and including legacy_stdio_definitions.lib is definitely the easier option.