Platform: add a WinSDK submodule

This adds ToolHelp32 to the WinSDK module which is needed for
snapshotting process state.  This is useful for tooling like
swift-inspect.

Author: compnerd

stdlib/public/Platform/winsdk.modulemap

@@ -411,6 +411,13 @@ module WinSDK [system] {
     link "sensorsapi.lib"
   }
 
+  module ToolHelp {
+    header "TlHelp32.h"
+    export *
+
+    link "kernel32.Lib"
+  }
+
   module UI {
     module XAML {
       module Hosting {