Convert skcms to only export functions (not data)

This simplifies shared library builds on Windows (no need to
conditionally change declspec to dllimport).

Once this lands, we can make the same change (plus update
internal references):
    https://skia-review.googlesource.com/c/skcms/+/124982

Change-Id: I0d4fa9031258f77d370e6e6e018afaf543c29d85
Reviewed-on: https://skia-review.googlesource.com/124983
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
4 files changed