Is this not helpful?
https://wiki.documentfoundation.org/Development/BuildingOnWi...
LibreOffice has official Windows builds, so I would expect that they can already build the software on Windows.
I'd rather use a toolchain I know better. In fact, I'd love to use clang on Windows.
I mean, sure, but (unless things have changed dramatically in the many years since I was a Windows dev) you don't have to do anything more than install VS. The compilers and nmake can be used without opening the GUI. IIRC, you can feed a VS project file (or -I'm pretty sure- a solution file) to nmake and get the same result you'd get from loading the GUI and pressing build.
[0] I do know that they are both parts of the VS build tooling. ;)