Also, tweak run.go to use no more than 2x the
number of CPUs, and only one on ARM.
53.85u 13.33s 53.69r ./run
50.68u 12.13s 18.85r go run run.go
Fixes#2833.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5754047
To find test files with legacy headers.
We can remove this flag once everything is converted.
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5694060