Moving to Visual Studio toolchain vc142

Microsoft has deprecated the Visual Studio (VS) 2017 compiler and removed it from all the CI they control (notably Azure Pipelines & Github Actions). This means that the default toolchain (== C/C++ compiler, linker, standard libraries, and related utilities) of that VS version - vc141 - is getting less and less use in upstream libraries (because public hosted CI doesn't use it anymore by default), and therefore support for it is bitrotting at an accelerating pace. We are therefore planning to move our toolchain on windows to vc142 (the default in VS2019) in two weeks, on 2022-08-25.

This will not affect you as a general user of conda-forge packages on windows; the only impact is that if you are locally compiling against artefacts produced by conda-forge and are still using VS2017 yourself, you will need to upgrade your compiler (VS2019 is a drop-in replacement & ABI-compatible).