CMake: Set _WIN32_WINNT=0x0601

[past-due]

This seems to have been added back in #327, and set to 0x0602 (Windows 8) as the target minimum Windows version.

However, all used Windows APIs are compatible with Windows 7 (and some folks still need to target Windows 7), so this PR updates _WIN32_WINNT to 0x0601 (Windows 7).

[saghul]

The problem is windows 7 is rol and there is no easy way to test in a ci to make sure we don't break it.

[past-due]

The problem is windows 7 is rol and there is no easy way to test in a ci to make sure we don't break it.

That’s part of the benefit: By setting _WIN32_WINNT=0x0601, there will be a compile error if someone tries to use an API (or new Windows API flag, etc) that isn't available on Windows 7. (Caught by the existing CI runs.) This helps provide a lot of assurance that it doesn't get broken.

(Hence why the MS recommendation is to set it to the minimum operating system version that the code is intended to support.)

[saghul]

I understand but I don't know if we want to be beholden to an operating system that is EOL already.

I'd be ok landing this today, with a big warning: the moment it becomes problematic we take it out.

@bnoordhuis thoughts?

[bnoordhuis]

The number of people that still seem to use Windows 7 in this day and age never ceases to surprise me... but anyway.

If we set that in CMakeLists.txt, readers will reasonably assume we support Windows 7 when we don't. Even Windows 8 is already stretching it.

If @saghul is okay with landing this, then I won't block it, but by myself I would've probably rejected it.

[saghul]

Let's give it a try.