Point external win build docs directly to internal win build docs

R=dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2630463002
Cr-Commit-Position: refs/heads/master@{#443068}

docs/windows_build_instructions.md

@@ -6,7 +6,7 @@ There are instructions for other platforms linked from the
 ## Instructions for Google Employees
 
 Are you a Google employee? See
-[go/building-chrome](https://goto.google.com/building-chrome) instead.
+[go/building-chrome-win](https://goto.google.com/building-chrome-win) instead.
 
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