O_SYNC changes only on linux-arm (and linux-arm-cgo), but
changes to match O_SYNC on linux-{386,amd64} and what Linux
upstream now uses. See discussion and links on
https://golang.org/cl/13261050/
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/13575045
This CL breaks Go 1 API compatibility but it doesn't matter because
previous ListenUnixgram doesn't work in any use cases, oops.
The public API change is:
-pkg net, func ListenUnixgram(string, *UnixAddr) (*UDPConn, error)
+pkg net, func ListenUnixgram(string, *UnixAddr) (*UnixConn, error)
Fixes#3875.
R=rsc, golang-dev, dave
CC=golang-dev
https://golang.org/cl/6937059