runtime: fix gogetenv on Plan 9

LGTM=rsc
R=rsc, ality
CC=golang-codereviews
https://codereview.appspot.com/137030043

Committer: Russ Cox <rsc@golang.org>
runtime/pprof: adjust cpuHogger so that tests pass on windows builders

LGTM=rsc
R=dvyukov, rsc
CC=golang-codereviews
https://codereview.appspot.com/140110043

Committer: Russ Cox <rsc@golang.org>