And if you're working on a cross-platform project, it's probably using CMake or something similar. The development cycle of `cmake .. && make` is simple and easy. As far as I could tell, Windows builds were not as straightforward. It's been awhile so maybe they've improved it, but I would hardly call their developer tools "unequaled"
I just want to install Clang in a straightforward manner, call the above-mentioned `cmake .. && make`, and have an exe waiting for me. Is that possible now? It wasn't in the past which is why I'm highly suspicious of your "hands down developer friendly" comment. Windows always seems to be the platform that has to do things slightly different, and has offered the most friction when developing projects that run on OS X, Linux, and Windows.
EDIT: I would also like to add that most CI services offer at least G++ or Clang++. AppVeyor seems to support Windows builds with MSVC but isn't free. This is yet another hindrance to smooth cross-platform development.