Add dev-qt from an older version of the gentoo repo

Qt5 has been removed, we restore it since we still use it.

dev-qt/qtx11extras/Manifest

@@ -0,0 +1 @@
+DIST qtx11extras-everywhere-opensource-src-5.15.18.tar.xz 123980 BLAKE2B 30b23aeea766d694c7b9097ba655ed2a3057543a58ab937925b0725af53676cf3490ec2c0eb1c69b353c1dcf34e8c7d5f2107e965617d1622b36f67120d0972b SHA512 7e12f87da4a2c8333adc09f0069cfdbb6b81e778b0e261b13a8631a90bc21deb831fc4d74229e977afa864919ef6dbe98fc37ef29eeffee52cacef21af4216f7

dev-qt/qtx11extras/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="project">
+		<email>qt@gentoo.org</email>
+		<name>Gentoo Qt Project</name>
+	</maintainer>
+	<upstream>
+		<bugs-to>https://qt-project.atlassian.net/</bugs-to>
+		<doc>https://doc.qt.io/</doc>
+	</upstream>
+	<slots>
+		<subslots>
+			Must only be used by packages that are known to use private parts of the Qt API.
+		</subslots>
+	</slots>
+</pkgmetadata>

dev-qt/qtx11extras/qtx11extras-5.15.18.ebuild

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+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+inherit qt5-build
+
+DESCRIPTION="Linux/X11-specific support library for the Qt5 framework"
+
+if [[ ${QT5_BUILD_TYPE} == release ]]; then
+	KEYWORDS="amd64 arm arm64 ~hppa ~loong ppc ppc64 ~riscv x86"
+fi
+
+IUSE=""
+
+RDEPEND="
+	=dev-qt/qtcore-${QT5_PV}*
+	=dev-qt/qtgui-${QT5_PV}*[X]
+"
+DEPEND="${RDEPEND}
+	test? ( =dev-qt/qtwidgets-${QT5_PV}* )
+"