Future-proof vs_toolchain.py for VS2019.

In trying to figure out an ARM64 builder issue, I tried VS2019. That
didn't fix the ARM64 issue, but it did reveal that I ported over some of
the logic from Chromium wrong. For "new-style" paths, the toolchain
directory should be toolchain_data['path'], not the parent directory of
win_sdk.

(The latest VS2019 package in Chromium puts win_sdk a few directories
down from the toolchain root.)

This CL should be a no-op for now because all our current toolchains use
Chromium's "old-style" win_sdk-relative paths.

Change-Id: I8ad7784abb479d1ede3995a44433e57448e8debf
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/45744
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

util/bot/vs_toolchain.py

diff --git a/util/bot/vs_toolchain.py b/util/bot/vs_toolchain.py
index c15df49..904f3ca 100644
--- a/util/bot/vs_toolchain.py
+++ b/util/bot/vs_toolchain.py
@@ -34,9 +34,8 @@
     # Old-style paths were relative to the win_sdk\bin directory.
     json_relative_dir = os.path.join(sdk_dir, 'bin')
   else:
-    # New-style paths are relative to the toolchain directory, which is the
-    # parent of the SDK directory.
-    json_relative_dir = os.path.split(sdk_dir)[0]
+    # New-style paths are relative to the toolchain directory.
+    json_relative_dir = toolchain_data['path']
   for k in env:
     entries = [os.path.join(*([json_relative_dir] + e)) for e in env[k]]
     # clang-cl wants INCLUDE to be ;-separated even on non-Windows,