runtime: drop CLONE_PARENT
runtime: drop CLONE_PARENT

The functionality we want (shared ppid) is implied
by CLONE_THREAD already, and CLONE_PARENT
causes problems if the Go program is pid 1 (init).

See issue 1406 for more details.

Fixes issue 1406.

R=adg, iant
CC=golang-dev
http://codereview.appspot.com/3971044

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