Needless to say that jpeg-9c is not in tree yet and jpeg-9 seems to be hopeless anyway (see bug 479818).
Not sure of the best solution yet.
The bug has been referenced in the following commit(s):
Author: Andreas Sturmlechner <email@example.com>
AuthorDate: 2018-02-01 23:17:26 +0000
Commit: Andreas Sturmlechner <firstname.lastname@example.org>
CommitDate: 2018-02-03 00:29:05 +0000
media-libs/jpeg: 9c version bump
Package-Manager: Portage-2.3.22, Repoman-2.3.6
media-libs/jpeg/Manifest | 1 +
media-libs/jpeg/jpeg-9c.ebuild | 71 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 72 insertions(+)}
*** Bug 646930 has been marked as a duplicate of this bug. ***
Considering this fixed jpeg-9c is now stable on all relevant arches.