They didn't really break anything, but I noticed that they added a bunch of include dirs that only exists on the unix side in an rntcl setup. Needless to say, such dirs aren't applicable.
My guess is that the Windows_NT test is a hack to disable that check in rntcl setups, but I haven't investigated the origin. If my guess is correct then it'd be better to instead check if $CC specifies rntcl or rntecl.