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 But that repo is out of date.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>
diff --git a/dev-util/opencl-headers/Manifest b/dev-util/opencl-headers/Manifest
new file mode 100644
index 0000000..fe202eb
--- /dev/null
+++ b/dev-util/opencl-headers/Manifest
@@ -0,0 +1 @@
+DIST opencl-headers-2021.04.29.tar.gz 59775 BLAKE2B 9e1728ce33066430711de911f4b2713abca5a0a57b8e52cb662aabe37657c703ab39dbbd990332847ae3d9f31f4855708c17832b801f8ca6a6f12ab12b139711 SHA512 370d02044c61f2394e9a8a9772b30b996074e3b51461387a570aaf1c29488844fe9090d873b2679eb4a472135bac7a9ba5590daf9d79c006de17f709afcb74e1
diff --git a/dev-util/opencl-headers/metadata.xml b/dev-util/opencl-headers/metadata.xml
new file mode 100644
index 0000000..40897a6
--- /dev/null
+++ b/dev-util/opencl-headers/metadata.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
+<pkgmetadata>
+	<maintainer type="person">
+		<email>marecki@gentoo.org</email>
+		<name>Marek Szuba</name>
+	</maintainer>
+	<longdescription lang="en">
+		The OpenCL API headers in this package are unified headers and are designed to work
+		with all released OpenCL versions. This differs from previous OpenCL API headers,
+		where version-specific API headers either existed in separate branches, or
+		in separate folders in a branch.
+
+		By default, the OpenCL API headers in this repository are for the latest OpenCL
+		version supported. To use these API headers to target a different OpenCL version,
+		an application may #define the preprocessor value CL_TARGET_OPENCL_VERSION before
+		including the OpenCL API headers. The CL_TARGET_OPENCL_VERSION is a three digit
+		decimal value representing the OpenCL API version.
+	</longdescription>
+	<upstream>
+		<remote-id type="github">KhronosGroup/OpenCL-Headers</remote-id>
+	</upstream>
+</pkgmetadata>
diff --git a/dev-util/opencl-headers/opencl-headers-2021.04.29.ebuild b/dev-util/opencl-headers/opencl-headers-2021.04.29.ebuild
new file mode 100644
index 0000000..5a30d0b
--- /dev/null
+++ b/dev-util/opencl-headers/opencl-headers-2021.04.29.ebuild
@@ -0,0 +1,25 @@
+# Copyright 1999-2021 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=7
+
+MY_PN="OpenCL-Headers"
+MY_P="${MY_PN}-${PV}"
+
+DESCRIPTION="Unified C language headers for the OpenCL API"
+HOMEPAGE="https://github.com/KhronosGroup/OpenCL-Headers"
+SRC_URI="https://github.com/KhronosGroup/${MY_PN}/archive/v${PV}.tar.gz -> ${P}.tar.gz"
+
+LICENSE="Apache-2.0"
+SLOT="0"
+KEYWORDS="*"
+
+# CHROMIUM: We stopped installing the CL headers from our custom ebuild.
+RDEPEND="!<=x11-drivers/opengles-headers-0.0.1-r36"
+
+S="${WORKDIR}/${MY_P}"
+
+src_install() {
+	insinto /usr/include
+	doins -r "${S}"/CL
+}