DO NOT MERGE: Testing SCons 4.4.0 with multiple MSVC toolsets

[bryanwweber]

Changes proposed in this pull request

If applicable, fill in the issue number this pull request is fixing

Closes #

If applicable, provide an example illustrating new features this pull request is introducing

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[ischoegl]

@bryanwweber ... are you still working on this? Otherwise, I may take a stab ...

[bryanwweber]

@ischoegl I'm not, I don't have a Windows machine to do rapid iterations, but the changes here should be a good start to what you need: https://github.com/Cantera/cantera/pull/1392/files#diff-d78c5c377c03dd251edc72cdb0ae7d9986fa08361eb392187218f8c670c0bc4eR170

Edit to add: I was trying to test and make sure that we got the correct behavior for SCons <4.4.0 when the new MSVC_TOOLSET_VERSION was introduced.

Feel free to close this if/when you push up a new branch 😄

[bryanwweber]

Superseded by #1404