We no longer really use platforms where CAS is unavailable.
Created attachment 261757 [details]
The main side effect of this is that this enables parallel GC on Windows. I don't see anything POSIX-specific in our parallel GC implementation, so I think that this is OK.
Comment on attachment 261757 [details]
Created attachment 261760 [details]
patch for landing
Fixes Windows, hopefully.
basic browsing on windows seems to work as well as it does without this patch.
Landed in http://trac.webkit.org/changeset/190131