@nnposter We skipped over VS 2010 in our own builds, so we did not encounter this problem, but we ran into other problems on VS 2013. As a workaround, we added the _MSC_VER check in nbase_winunix.h which seems to be working well. Could you try changing the version there from "1800" (VS 2013) to "1600" (VS 2010) and see if it solves the problem? Otherwise, we'll apply your fix.
Sourcing errno.h (by changing the _MSC_VER condition) takes care of the missing EOPNOTSUPP but it exposes the class/struct bug that Gisle recently reported, which was until then latent. Applying his fix makes everything compile without errors.
It seems to me that perhaps both changes (the conditional and the custom definition) should be applied. Otherwise we would not be treating the error codes consistently, such as EOPNOTSUPP vs EMSGSIZE.