runtime: fix data race in Plan9 sysalloc Add mutex to protect brk limit. Add mstats.sys update.
runtime: fix data race in Plan9 sysalloc
Add mutex to protect brk limit.
Add mstats.sys update.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4762045

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

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go