> Is it a warning or an error? What is the warning/error message? What is your buildbot?

It is a compiler error as you point out below (with message).  By buildbot is:

https://buildbot.python.org/all/#/workers/12

> Right now, it seems like only "AMD64 Windows7 SP1 3.x" is still red:
>
> "2>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Platforms\x64\PlatformToolsets\v140\Toolset.targets(36,5): error MSB8036: The Windows SDK version 10.0.17134.0 was not found. Install the required version of Windows SDK or change the SDK version in the project property pages or by right-clicking the solution and selecting "Retarget solution". [C:\buildbot.python.org\3.x.kloth-win64\build\PCbuild\pythoncore.vcxproj]"
>
> https://buildbot.python.org/all/#/builders/40/builds/1322
>
> Are you talking about this error?

All the builders on my buildbot can no longer find a matching SDK
version due to how the SDK version detection is handled.  Previously,
my buildbot had VS2015.2 installed whose build tools (version 1.2)
didn't use the property `DefaultWindowsSDKVersion` to select the SDK
version and just defaulted to Windows 8.1 SDK.  Now that I've updated
to VS2015.3 (includes build tools 1.4) it *does* use this property to
select the SDK version.  However, I have a newer SDK installed than is
listed in the hard-coded list so it defaults to highest one in the
list causing the missing SDK error.

This PR changes the detection logic to simply accept what SDK the user
has installed as long as it is newer (or the same) as the minimum
allowed version.

For those versed in MSBuild, this should be fairly self-evident, but
hopefully this helps those who are not :)