AGPL only differs from GPL with regard to services provided over networks, which doesn't really apply here. Beyond that, AGPL is no more viral than GPL. So "there's no linking exception in the AGPL" is really irrelevant considering that there isn't one in GPL either, and I'm sure Google uses GCC.

Yes, there's a stigma against AGPL, but a blanket policy against using AGPL'ed software will occasionally ban something totally unproblematic, which is the case here.