env/windows: download archived vs_buildtools.exe

Change startup.ps to download an archived copy of vs_buildtools.exe
from our GCS bucket as opposed to downloading off the net from
https://aka.ms/vs/15/release (to avoid any surprises).

Updates golang/go#35006.

Change-Id: I30fa5aae1281f694a90241f34d82288ab54dd0ba
Reviewed-on: https://go-review.googlesource.com/c/build/+/406855
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>
diff --git a/env/windows/startup.ps1 b/env/windows/startup.ps1
index 5be2c5a..789fd0d 100644
--- a/env/windows/startup.ps1
+++ b/env/windows/startup.ps1
@@ -148,7 +148,7 @@
 # https://docs.microsoft.com/en-us/visualstudio/install/build-tools-container
 Write-Host "downloading Visual Studio Build Tools"
 $vs_buildtools = "$builder_dir\vs_buildtools.exe"
-Get-FileFromUrl -URL "https://aka.ms/vs/15/release/vs_buildtools.exe" -Output "$vs_buildtools"
+Get-FileFromUrl -URL "https://storage.googleapis.com/go-builder-data/vs_buildtools.exe" -Output "$vs_buildtools"
 
 Write-Host "installing Visual Studio Build Tools"
 & $vs_buildtools --quiet --wait --norestart --nocache --installPath "$dep_dir\vs" --all