runtime: duplicate code for runtime.nanotime to avoid stack overflow in vDSO clock_gettime Fixes issue 4402.
runtime: duplicate code for runtime.nanotime to avoid stack overflow in vDSO clock_gettime
Fixes issue 4402.

R=remyoudompheng, shivakumar.gn, random0x00, rsc
CC=golang-dev
http://codereview.appspot.com/6842063

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