runtime: introduce typedefs and delete struct keywords in mgc0.c
runtime: introduce typedefs and delete struct keywords in mgc0.c

R=rsc
CC=golang-dev
https://codereview.appspot.com/7029055

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go