TLS fix

scripts/VcpkgPowershellUtils.ps1

@@ -1,4 +1,3 @@
-[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
 function vcpkgHasModule([Parameter(Mandatory=$true)][string]$moduleName)
 {
     return [bool](Get-Module -ListAvailable -Name $moduleName)
@@ -121,11 +120,26 @@ function vcpkgDownloadFile( [Parameter(Mandatory=$true)][string]$url,
         return
     }
 
+    if ($url -match "github")
+    {
+        if ([System.Enum]::IsDefined([Net.SecurityProtocolType], "Tls12"))
+        {
+            [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
+        }
+        else
+        {
+            Write-Warning "Github has dropped support for TLS versions prior to 1.2, which is not available on your system"
+            Write-Warning "Please manually download $url to $downloadPath"
+            throw "Download failed"
+        }
+    }
+
     vcpkgCreateParentDirectoryIfNotExists $downloadPath
 
     $downloadPartPath = "$downloadPath.part"
     vcpkgRemoveItem $downloadPartPath
 
+
     $wc = New-Object System.Net.WebClient
     if (!$wc.Proxy.IsBypassed($url))
     {