I combined two answers (@bviktor and @jocassid). It was tested on Windows 10 and Windows Server 2012.
function New-SymLink ($link, $target)
{
if ($PSVersionTable.PSVersion.Major -ge 5)
{
New-Item -Path $link -ItemType SymbolicLink -Value $target
}
else
{
$command = "cmd /c mklink /d"
invoke-expression "$command ""$link"" ""$target"""
}
}