cmd/cgo: makes clang happy by not using __gcc_struct__ attribute.
cmd/cgo: makes clang happy by not using __gcc_struct__ attribute.

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/10150043

apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,gnanderson/go,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,gnanderson/go,tv42/old-go,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,apparentlymart/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme