Install this version:
emerge -a =dev-libs/olm-3.1.4
If this version is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask =dev-libs/olm-3.1.4
Or alternatively:
emerge --autounmask-write -a =dev-libs/olm-3.1.4
# Copyright 1999-2019 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
EAPI=8
inherit cmake-multilib
DESCRIPTION="An implementation of the Double Ratchet cryptographic ratchet in C++"
HOMEPAGE="https://gitlab.matrix.org/matrix-org/olm/"
if [[ ${PV} != "9999" ]]; then
KEYWORDS="~amd64 ~x86"
fi
SRC_URI="https://gitlab.matrix.org/matrix-org/${PN}/-/archive/${PV}/${P}.tar.bz2"
LICENSE="GPL-3"
SLOT="0"
IUSE=""
RDEPEND=""
DEPEND="${RDEPEND}"