dev-libs/cJSON: Add from Gentoo

It's from Gentoo commit ce2861de5c1921bcde21f9cd4f0ce961d8fd61be.

sdk_container/src/third_party/portage-stable/dev-libs/cJSON/Manifest

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+DIST cJSON-1.7.15.tar.gz 352278 BLAKE2B e0de3b8d56020853d56f5512e6e7216adafd238b6f69bbf6965b153bfe8ebfc23593dfa7cfb8543d8730d90820153d263c8af276c8e9588ba8a5ad76a50f8b72 SHA512 0b32a758c597fcc90c8ed0af493c9bccd611b9d4f9a03e87de3f7337bb9a28990b810befd44bc321a0cb42cbcd0b026d45761f9bab7bd798f920b7b6975fb124

sdk_container/src/third_party/portage-stable/dev-libs/cJSON/cJSON-1.7.15.ebuild

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+# Copyright 2021-2022 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=7
+
+inherit cmake
+
+DESCRIPTION="Ultralightweight JSON parser in ANSI C"
+HOMEPAGE="https://github.com/DaveGamble/cJSON"
+SRC_URI="https://github.com/DaveGamble/${PN}/archive/v${PV}.tar.gz -> ${P}.tar.gz"
+
+LICENSE="MIT"
+SLOT="0"
+KEYWORDS="~alpha amd64 arm arm64 ~hppa ~ia64 ppc ppc64 ~riscv sparc x86"
+IUSE="test"
+RESTRICT="!test? ( test )"
+
+src_prepare() {
+	cmake_src_prepare
+
+	sed -i -e '/-Werror/d' CMakeLists.txt || die
+}
+
+src_configure() {
+	local mycmakeargs=(
+		-DENABLE_CJSON_TEST=$(usex test)
+	)
+
+	cmake_src_configure
+}

sdk_container/src/third_party/portage-stable/dev-libs/cJSON/metadata.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE pkgmetadata SYSTEM "https://www.gentoo.org/dtd/metadata.dtd">
+<pkgmetadata>
+  <maintainer type="person">
+    <email>mattst88@gentoo.org</email>
+    <name>Matt Turner</name>
+  </maintainer>
+  <upstream>
+    <remote-id type="github">DaveGamble/cJSON</remote-id>
+  </upstream>
+</pkgmetadata>