cmd/prof: don't build on Plan 9 for now.
cmd/prof: don't build on Plan 9 for now.

R=golang-dev, bradfitz, akumar
CC=golang-dev
http://codereview.appspot.com/5629054

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