I modified the poco-1.9.0 ebuild to accept openssl 1.1.x as a dependency and the package built properly. Noting that the older poco versions can depend on the newer openssl version, this is probably a safe change.
This is probably the correct fix. Judging from the upstream bug report at https://github.com/pocoproject/poco/issues/1376 it looks like openssl 1.1.x should be supported from about poco 1.7.9 onwards. In fact, it appears that at least one feature in 1.9.0 (preliminary TLS 1.3 support) is only available when built against 1.1.1 or later.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=9cb889f92a3eba8a498804cec6d516c8912331d9 commit 9cb889f92a3eba8a498804cec6d516c8912331d9 Author: Pacho Ramos <pacho@gentoo.org> AuthorDate: 2019-03-23 12:24:17 +0000 Commit: Pacho Ramos <pacho@gentoo.org> CommitDate: 2019-03-23 12:25:16 +0000 dev-libs/poco: Fix deps, drop dead apache support Closes: https://bugs.gentoo.org/675052 Closes: https://bugs.gentoo.org/673158 Closes: https://bugs.gentoo.org/658202 Closes: https://bugs.gentoo.org/620224 Package-Manager: Portage-2.3.62, Repoman-2.3.12 Signed-off-by: Pacho Ramos <pacho@gentoo.org> dev-libs/poco/poco-1.9.0-r2.ebuild | 131 +++++++++++++++++++++++++++++++++++++ 1 file changed, 131 insertions(+)