misc/cgo/test: test recursive internal OS thread lock
misc/cgo/test: test recursive internal OS thread lock

This would have failed with CL 11663043.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/11480045

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang