In cl/8652 I broke darwin/arm and darwin/386 because I removed the *g
parameter, which they both expect and use. This CL adjusts both ports
to look for g0 in m, just as darwin/amd64 does.

Tested on darwin{386,arm,amd64}.

Change-Id: Ia56f3d97e126b40d8bbd2e8f677b008e4a1badad
Reviewed-on: https://go-review.googlesource.com/8666Reviewed-by: Ian Lance Taylor <iant@golang.org>