update Win/Android toolchain setup after rolling GN

The new GN doesn't like "ar = ar + ...", etc.

CQ_INCLUDE_TRYBOTS=skia.primary:Build-Win-Clang-arm64-Release-Android

Change-Id: Ib131ee367c4af144f8ffb8562fc26b67675e4f45
Reviewed-on: https://skia-review.googlesource.com/5726
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed