base: Explicitly mark Data.Either.{left,right} as INLINABLE
Test Plan: read it
Reviewers: dfeuer, austin, hvr, nomeata
Reviewed By: dfeuer, nomeata
Subscribers: nomeata, rwbarton, thomie
GHC Trac Issues: Trac #13689
Differential Revision: https://phabricator.haskell.org/D3576