The point is just that: Right now I can write assembly that will work on GDC, LDC, and DMD on non-Windows. It will not work for DMD on Windows. Something has to change here.
If it doesn't work on Windows, it should be versioned out. What we have: http://dlang.org/version.html#PredefinedVersions - versions for LDC, GDC, DMD and Windows - all what you want.
