misc/dist: build race packages when os suffix present
misc/dist: build race packages when os suffix present

The "darwin-amd64-osx10.8" target was not matching "darwin-amd64".

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/14930043

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