Update DEPS: roll spirv-tools and spirv-headers.

spirv-tools and spirv-headers were about two years out-of-date, and
Dawn requires more recent versions.

This required an updated BUILD.gn file for spirv-tools. I used a
modified version of the one I had written for Dawn. (The latter will
be removed in favour of this one when we switch the Dawn backend
from using Dawn's DEPS for spirv-tools and spirv-headers to using
Skia's).

Change-Id: If61eb05ada9f4287b1a16daf10f9b1fac041a7b0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234907
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
3 files changed