Some revdeps may require absl built with -DCMAKE_CXX_STANDARD=17
Normally that should not be a useflag, but we need to expose it to
package-manager so other packages can depend on it.
Upstream insist on using cmake for that and not proper headers...
Package-Manager: Portage-3.0.8, Repoman-3.0.2
Signed-off-by: Georgy Yakovlev <gyakovlev@gentoo.org>
6ddbca2126