api: add Linux/ARM to go1 API

It's very unfortunate that the type of Data field of struct
RawSockaddr is [14]uint8 on Linux/ARM instead of [14]int8
on all the others.
btw, it should be [14]int8 according to my header files.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6275050

src/cmd/api/goapi.go

@@ -51,6 +51,7 @@ var contexts = []*build.Context{
 	{GOOS: "linux", GOARCH: "386"},
 	{GOOS: "linux", GOARCH: "amd64", CgoEnabled: true},
 	{GOOS: "linux", GOARCH: "amd64"},
+	{GOOS: "linux", GOARCH: "arm"},
 	{GOOS: "darwin", GOARCH: "386", CgoEnabled: true},
 	{GOOS: "darwin", GOARCH: "386"},
 	{GOOS: "darwin", GOARCH: "amd64", CgoEnabled: true},