dev-util/opencl-headers: Import from upstream

We've been installing the OpenCL headers from our custom repo at
src/third_party/khronos. But that repo is out of date.

As precedent, we've already done the migration for
dev-util/spirv-headers, and have always used dev-util/vulkan-headers.

Add a RDEPEND blocker to work around file conflicts, as explained in
<https://chromium.googlesource.com/chromiumos/docs/+/main/portage/ebuild_faq.md#How-do-I-handle-file-collisions>.

BUG=none
TEST=emerge-$BOARD opengles-headers opencl-headers

Cq-Depend: chromium:3149592
Change-Id: Id7f559851be2bccbcc9b6e837a4cfdb3f809b31b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/3149593
Tested-by: Chad Versace <chadversary@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Romaric Jodin <rjodin@chromium.org>
Commit-Queue: Chad Versace <chadversary@chromium.org>
3 files changed