runtime: use SYSCALL instead of INT 0x80 in FreeBSD's runtime.osyield on amd64
runtime: use SYSCALL instead of INT 0x80 in FreeBSD's runtime.osyield on amd64

R=mikioh.mikioh, rsc
CC=golang-dev
http://codereview.appspot.com/5690062

Committer: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>

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