MSVC tool supports choosing specific msvc version down to minor version

[dmoody256]

Newer versions of Visual Studio support installing multiple minor versions of the MSVC toolset: https://blogs.msdn.microsoft.com/vcblog/2017/11/15/side-by-side-minor-version-msvc-toolsets-in-visual-studio-2017/

The default or latest MSVC version can be found in Auxiliary\Build\Microsoft.VCToolsVersion.default.txt, and the new vcvar batch scripts allow you to pass the minor version as an option.

SCons could support this, by allowing the minor version to be set in the enivornment, something like env['MSVC_SPECIFIC_VERSION']='14.11.1673' and then passing that along to the vcvar script call.

A TODO was introduced in #3264.

[bdbaddog]

I'm thinking MSVC_VERSION= allowing more than just MM.mm and then would do a left string match
so 14.11 would match 14.11.1673 and 14.11., 14.11.1 would match 14.11.1. so split on '.' and then match pieces as far as the request.

That way no new variable needed. No change to existing build systems which don't need that specific.

Thoughts?

[mwichmann]

We can do this now, right? @jcbrill ?

[jcbrill]

We can do this now, right?

It is is possible to do now.

However, likely the "best" method for an end user is not implemented yet but is on the radar.

See linked comment for the gory details:
#3664 (comment)

[bdbaddog]

Fixed In #4174