This CL adds TCPInfo struct to linux/386,arm.
It's already added to linux/amd64.

Note that not sure the reason but cgo godefs w/ latest gcc
translates a flexible array member in structures correctly,
handles it as a non-incomplete, non-opaque type, on Go 1.
This CL reverts such changes by hand for the Go 1 contract.

R=minux.ma, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/7197046