cmd/pprof: exit with non-zero status code on error

Set the status code in case of error.

Fixes #11510

Change-Id: If461c30a1f6d2275539f33a2eabd7b19bbfa411d
Reviewed-on: https://go-review.googlesource.com/16718
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/pprof/pprof.go

@@ -27,6 +27,7 @@ func main() {
 	var extraCommands map[string]*commands.Command // no added Go-specific commands
 	if err := driver.PProf(flags{}, fetch.Fetcher, symbolize, new(objTool), plugin.StandardUI(), extraCommands); err != nil {
 		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(2)
 	}
 }