On the other hand, clang is very much a second class citizen on Windows.

Every compiler that is not (and some may even consider it second class considering its UX) MSVC is a second class citizen on Windows.

True, but is gcc much better, or does chrome use visual studio? (I honestly don't know, wondered if anyone else did)

Yes.

I don't use the MSVC toolchain or Windows for that matter, so I don't have a good compass for this, but the impression from the newsletter, dev meetings etc is that clang-cl is constantly being improved. Is the situation still that poor?

They have a site covering compatibility with MSVC: http://clang.llvm.org/docs/MSVCCompatibility.html

I think it's pretty acceptable, if you're writing C. As you can see, C++ support is only partially completed (no exceptions!). But you're right, Clang on Windows gets constantly improved.

The creation of good debugging information (MSVC's /Zi or even /ZI option) is also missing. For a first class citizen, support of the (undocumented) PDB format is a requirement in my opinion.

So is GCC. Perhaps it's still one less compiler to deal with, if they don't need GCC on any platform any more.

???? Compared to GCC?

You can now build a fairly well-functioning chrome binary, from visual studio, with clang/llvm, without source code changes.