runtime: disable Native Client fake time support
runtime: disable Native Client fake time support

This CL is a reformulation of CL 73110043 containing only the minimum required to get the nacl builds compiling.

LGTM=bradfitz
R=rsc, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/74220043

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