[bazel] Add macOS toolchain.

This CL copies the Skia macOS Bazel toolchain into the SkCMS repository.

I tested this toolchain by running the following commands on my M1 Macbook Pro:

    $ bazel build //...
    $ bazel test //...

Bazel might take several minutes to download the toolchain the first time it runs.

Note that "bazel test //..." reports the following test failure:

    expect(1.000001f < skcms_TransferFunction_eval(&dec, skcms_TransferFunction_eval(&enc, 1.000001f))) failed at tests.c:1545

Bug: b/307796721
Change-Id: I000057f1a1dc186d26af6abd232e73b92e292ae9
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/770875
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Leandro Lovisolo <lovisolo@google.com>
10 files changed