app-forensics/sleuthkit: force libewf to link against local deps

app-forensics/sleuthkit: force libewf to link against local deps

We bundle a legacy version of libewf since that's the only version the
upstream officially supports. It should link against the cross
platform libc* libraries supplied in the tarball and not use the
system ones. Currently, this has no visible impact for Gentoo users as
aformentioned libraries do not exist in the tree yet.

Suggested-by: Anton Bolshakov <blshkv@pentoo.ch>
Closes: https://bugs.gentoo.org/677252
Package-Manager: Portage-2.3.67, Repoman-2.3.12
Signed-off-by: Göktürk Yüksek <gokturk@gentoo.org>