[bazel] Sketch out changes for Mac toolchain

Change-Id: Idae84d8d9538012e5cfb75a1a477dbc72a4da5bc
Bug: skia:13125
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/526264
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>
7 files changed