cross-compile golang on Windows host

cross-build.ps1

$hostOS = Invoke-Expression "go env GOOS"
$hostARCH = Invoke-Expression "go env GOARCH"

$buildInfoDate = (Get-Date).ToString("yyyy-MM-dd_hh:mm")

# NOTE: don't use "arm64", since raspbian is 32-bit only, feb-2017
$env:GOOS = "linux"
$env:GOARCH = "arm"
$env:GOARM = "7"

Invoke-Expression "go build -v -ldflags '-X main.BuildInfoDate=$buildInfoDate' cmd/ex1/ex1.go"
if ($LastExitCode -ne 0) {
    Return
}

Remove-Item Env:\GOOS
Remove-Item Env:\GOARCH
Remove-Item Env:\GOARM

Write-Host "Uploading binary ..."
$uploadTime = Measure-Command {
    Invoke-Expression "scp ex1 breakout1:."
}
Write-Host "Upload took" $uploadTime.TotalSeconds "sec"

Invoke-Expression "ssh breakout1 chmod +x ./ex1"
# Invoke-Expression "ssh breakout1 ./ex1"