code review 69970044: syscall: workaround Dragonfly BSD kernel exec bug

syscall: workaround Dragonfly BSD kernel exec bug
See also CL 4259056 for FreeBSD.

Test program:
// exec.go
package main
import (
        "log"
        "os"
        "os/exec"
        "runtime"
)
func main() {
        path := runtime.GOROOT() + "/src/pkg/net/http/cgi/testdata"
        cmd := &exec.Cmd{
                Path:   "test.cgi",
                Args:   []string{path + "/test.cgi"},
                Dir:    path
                Stdout: os.Stdout}
        if err := cmd.Start(); err != nil {
                log.Fatal(err)
        }
        if err := cmd.Wait(); err != nil {
                log.Fatal(err)
        }
}

$ go run exec.go
2014/03/01 15:52:41 fork/exec test.cgi: argument list too long

[minux1, 2014-03-01 09:02:57]

Hello rsc@golang.org (cc: golang-codereviews@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go

[iant, 2014-03-01 23:00:00]

LGTM

[minux1, 2014-03-01 23:56:54]

*** Submitted as https://code.google.com/p/go/source/detail?r=6f7f3ab0292a ***

syscall: workaround Dragonfly BSD kernel exec bug
See also CL 4259056 for FreeBSD.

Test program:
// exec.go
package main
import (
        "log"
        "os"
        "os/exec"
        "runtime"
)
func main() {
        path := runtime.GOROOT() + "/src/pkg/net/http/cgi/testdata"
        cmd := &exec.Cmd{
                Path:   "test.cgi",
                Args:   []string{path + "/test.cgi"},
                Dir:    path
                Stdout: os.Stdout}
        if err := cmd.Start(); err != nil {
                log.Fatal(err)
        }
        if err := cmd.Wait(); err != nil {
                log.Fatal(err)
        }
}

$ go run exec.go
2014/03/01 15:52:41 fork/exec test.cgi: argument list too long

LGTM=iant
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/69970044

[gobot, 2014-03-02 00:26:46]

This CL appears to have broken the linux-amd64-race builder.

[minux1, 2014-03-02 00:30:05]

On Sat, Mar 1, 2014 at 7:26 PM, <gobot@golang.org> wrote:

> This CL appears to have broken the linux-amd64-race builder.
>
Data race in net/http, unrelated.

>
> https://codereview.appspot.com/69970044/
>