Make.pkg: use installed runtime.h for cgo
Make.pkg: use installed runtime.h for cgo

Fixes issue 1381.

R=r, r2
CC=golang-dev
http://codereview.appspot.com/3775050

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