I imagine the vast majority of cross-compiles for the core tasks that Go targets will be to x86 or ARM, which it does support well (from everything I've heard).
I remember some comments here on HN a few months back (maybe longer) about how there isn't really an "ARM" to target, as since there's such diversity in what an ARM chip can provide that it's hard to make assumptions about what you can rely on from just "ARM". I believe it was in response to what is available to help with booting the system, but I imagine it extends into what exactly your runtime can rely on.
