This reverts commit 13144d11c1.
It doesn't work.
Trying to open the solutions in Visual Studio results in
"libsodium.vcxproj(8,3): The element <#text> beneath element
<ItemGroup> is unrecognized."
* Retarget Visual studio tool chain to v142
* add ARM64 option to wintest.bat
* add windows/arm64 target to appveyor for CI
* add arm64 targets to visual studio solutions
* add cross compile option to wintest.bat
* Fix missing SET in wintest.bat
* update auto-generation scripts for msvc and update project files