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/qtserialport/qtserialport-5.15.16.ebuild

@@ -0,0 +1,29 @@
+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+inherit qt5-build
+
+DESCRIPTION="Serial port abstraction library for the Qt5 framework"
+
+if [[ ${QT5_BUILD_TYPE} == release ]]; then
+	KEYWORDS="amd64 arm arm64 ~hppa ~loong ppc ppc64 ~riscv x86"
+fi
+
+IUSE=""
+
+DEPEND="
+	=dev-qt/qtcore-${QT5_PV}*
+	virtual/libudev:=
+"
+RDEPEND="${DEPEND}"
+
+src_prepare() {
+	# make sure we link against libudev
+	sed -i -e 's/:qtConfig(libudev)//' \
+		-e "s/\$\$QMAKE_LIBS_LIBUDEV/-ludev/" \
+		src/serialport/serialport-lib.pri || die
+
+	qt5-build_src_prepare
+}