No PHP 7 support exists officially.
A fork at https://github.com/esminis/php_pecl_spl_types seems to have ported to 7,
but testing is needed.
Package-Manager: portage-2.3.2
--- /dev/null
+# Copyright 1999-2016 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+# $Id$
+
+EAPI=6
+
+PHP_EXT_NAME="spl_types"
+PHP_EXT_INI="yes"
+PHP_EXT_ZENDEXT="no"
+PHP_EXT_PECL_PKG="SPL_Types"
+
+USE_PHP="php5-6"
+
+inherit php-ext-pecl-r3
+
+KEYWORDS="~amd64 ~x86"
+
+DESCRIPTION="Standard PHP library types add-on"
+LICENSE="PHP-3"
+SLOT="0"
+IUSE=""
+
+RDEPEND=""
+DEPEND="${RDEPEND}"