% go version
go version go1.9.2 linux/amd64

% go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/kenhys/go"
GORACE=""
GOROOT="/home/kenhys/.anyenv/envs/goenv/versions/1.9.2"
GOTOOLDIR="/home/kenhys/.anyenv/envs/goenv/versions/1.9.2/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build954881475=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

% cat sample.go
package main

import (
        "golang.org/x/sys/windows"
        "log"
        "os/exec"
        "syscall"
)

func Launch(path string, args []string) {
        command := exec.Command(path, args...)
        // CREATE_BREAKAWAY_FROM_JOB = 0x01000000
        command.SysProcAttr = &syscall.SysProcAttr{CreationFlags: syscall.CREATE_BREAKAWAY_FROM_JOB}
        // Current workaround for CREATE_BREAKAWAY_FROM_JOB flag
        //command.SysProcAttr = &syscall.SysProcAttr{CreationFlags: 0x01000000}
        err := command.Start()
        if err != nil {
                log.Fatal(err)
        }
}

func main() {
        Launch("host.exe", []string{})
}

diff --git a/windows/types_windows.go b/windows/types_windows.go
index 78b714c..2ba3a7d 100644
--- a/windows/types_windows.go
+++ b/windows/types_windows.go
@@ -161,6 +161,7 @@ const (

        CREATE_NEW_PROCESS_GROUP   = 0x00000200
        CREATE_UNICODE_ENVIRONMENT = 0x00000400
+       CREATE_BREAKAWAY_FROM_JOB  = 0x01000000

        PROCESS_TERMINATE         = 1
        PROCESS_QUERY_INFORMATION = 0x00000400

+ gox -os=windows temp_sample/sample
Number of parallel builds: 7

-->   windows/amd64: temp_sample/sample
-->     windows/386: temp_sample/sample

2 errors occurred:
--> windows/386 error: exit status 2
Stderr: # temp_sample/sample
src/temp_sample/sample/sample.go:4:2: imported and not used: "golang.org/x/sys/windows"
src/temp_sample/sample/sample.go:13:60: undefined: syscall.CREATE_BREAKAWAY_FROM_JOB