[Issue 17999] UCRTVersion not properly set for Visual Studio Community 2017

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17999

--- Comment #2 from Bastiaan Veelo <Bastiaan at Veelo.net> ---
Use of the -m32mscoff option needs the same change under the
[Environment32mscoff] section.

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