Install the Windows toolchain under util/bot

Combined with https://crrev.com/c/5346536, this should, I believe, avoid
needing to re-download the toolchains over and over on every CI run once
the caches all fill.

Change-Id: I4991cf61dd164d7d39da91184ba7051ac59ce3f1
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/67347
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
diff --git a/.gitignore b/.gitignore
index d1cc3b8..439b6aa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,6 +26,7 @@
 /util/bot/sde-linux64.tar.xz
 /util/bot/sde-win32
 /util/bot/sde-win32.tar.xz
+/util/bot/win_toolchain
 /util/bot/win_toolchain.json
 
 # Ignore target under any directory.
diff --git a/util/bot/vs_toolchain.py b/util/bot/vs_toolchain.py
index d287ee2..c6dc4a4 100644
--- a/util/bot/vs_toolchain.py
+++ b/util/bot/vs_toolchain.py
@@ -12,6 +12,7 @@
 
 
 script_dir = os.path.dirname(os.path.realpath(__file__))
+toolchain_dir = os.path.join(script_dir, 'win_toolchain')
 json_data_file = os.path.join(script_dir, 'win_toolchain.json')
 
 
@@ -91,6 +92,7 @@
                   'win_toolchain',
                   'get_toolchain_if_necessary.py'),
       '--output-json', json_data_file,
+      '--toolchain-dir', toolchain_dir,
     ] + _GetDesiredVsToolchainHashes(version)
   subprocess.check_call(get_toolchain_args)
   return 0