syscall: Use vsyscall for syscall.Gettimeofday and .Time on linux amd64.
Ian Lance Taylor authored
Regenerate zsyscall_linux_*.go files with recent changes to
mksyscall.sh.

Add socketpair to syscall_linux_amd64.go; for some reason it
was in the generated file but not in the source file.

R=rsc, r2
CC=golang-dev
https://golang.org/cl/2190044
7d03d0ec