Bump CoreFx to rc2-23808

Workaround for issue 1294

Improve crossgen notifications

scripts/clean/clear-nuget-cache.ps1

@@ -0,0 +1,27 @@
+#
+# Copyright (c) .NET Foundation and contributors. All rights reserved.
+# Licensed under the MIT license. See LICENSE file in the project root for full license information.
+#
+
+. $PSScriptRoot\..\common\_common.ps1
+
+if ($env:CI_BUILD -eq "1") {
+    # periodically clear out the package cache on the CI server
+    $PackageCacheFile = "$env:NUGET_PACKAGES\packageCacheTime.txt"
+
+    if(!(Test-Path $PackageCacheFile)) {
+        Get-Date | Out-File -FilePath $PackageCacheFile
+    }
+    else {
+        $PackageCacheTimeProperty = Get-ItemProperty -Path $PackageCacheFile -Name CreationTimeUtc
+        $PackageCacheTime = [datetime]($PackageCacheTimeProperty).CreationTimeUtc
+
+        if ($PackageCacheTime -lt ([datetime]::UtcNow).AddHours(-$env:NUGET_PACKAGES_CACHE_TIME_LIMIT)) {
+            header "Clearing package cache"
+
+            Remove-Item -Recurse -Force "$env:NUGET_PACKAGES"
+            mkdir $env:NUGET_PACKAGES | Out-Null
+            Get-Date | Out-File -FilePath $PackageCacheFile
+        }
+    }
+}