pkgbase: Do record dependency on non-existent libelftc package

libelftc is an internal lib so it's never installed.
When building with WITH_MANSPLITPKG=yes the libelftc-man package
will have a dependecy on a non-existent libelftc package.

Sponsored by: Beckhoff Automation GmbH & Co. KG

(cherry picked from commit 65fa2fd23b9de1dd81a0a5fafc1d69757792edac)