utils: correctly stage MSMs for Windows Runtime

Ensure that we stage all the MSMs for the Windows Runtime distribution.
This enables us to consider online installers which would allow users to
select subsets of the installer to download when needed.

Author: compnerd

utils/build.ps1

@@ -3169,7 +3169,9 @@ function Build-Installer([Hashtable] $Platform) {
 function Copy-BuildArtifactsToStage([Hashtable] $Platform) {
   Copy-File "$BinaryCache\$($Platform.Triple)\installer\Release\$($Platform.Architecture.VSName)\*.cab" $Stage
   Copy-File "$BinaryCache\$($Platform.Triple)\installer\Release\$($Platform.Architecture.VSName)\*.msi" $Stage
-  Copy-File "$BinaryCache\$($Platform.Triple)\installer\Release\$($Platform.Architecture.VSName)\*.msm" $Stage
+  foreach ($SDKPlatform in $WindowsSDKPlatforms) {
+    Copy-File "$BinaryCache\$($Platform.Triple)\installer\Release\$($SDKPlatform.Architecture.VSName)\*.msm" $Stage
+  }
   Copy-File "$BinaryCache\$($Platform.Triple)\installer\Release\$($Platform.Architecture.VSName)\installer.exe" $Stage
   # Extract installer engine to ease code-signing on swift.org CI
   if ($ToBatch) {