[llvm] [llvm][docs] Note Windows on Arm setting in Visual Studio guide (PR #147710)

[David Spickett via llvm-commits]

DavidSpickett wrote:

I think this is an improvement over the current doc, even if it is leading people to use more options than they need to. So I'm going to merge this.

https://github.com/llvm/llvm-project/pull/147710