The flag seems obsolete now. When it's disabled, default standard is used (C++14-ish). When it's enabled, it causes *older* C++11 being enforced.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=9d4a85b0d543b4564beaaa955c2314e70b7e6952 commit 9d4a85b0d543b4564beaaa955c2314e70b7e6952 Author: Andreas Sturmlechner <asturm@gentoo.org> AuthorDate: 2020-03-22 00:31:58 +0000 Commit: Andreas Sturmlechner <asturm@gentoo.org> CommitDate: 2020-03-22 00:32:41 +0000 sci-libs/ceres-solver: Drop USE c++11 Closes: https://bugs.gentoo.org/705192 Package-Manager: Portage-2.3.94, Repoman-2.3.21 Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org> sci-libs/ceres-solver/ceres-solver-1.14.0.ebuild | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)