cmd/go: add -fno-common by default on Darwin         Fixes part of issue 3253.         We still need to support scattered relocations though.
cmd/go: add -fno-common by default on Darwin
        Fixes part of issue 3253.
        We still need to support scattered relocations though.

R=golang-dev, bsiegert, rsc, iant
CC=golang-dev
http://codereview.appspot.com/5822050

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang