User's guide: .a files can be 2-2.5x larger with -split-objs
User's guide: .a files can be 2-2.5x larger with -split-objs

And remove warning. This feature is available through cabal even.

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D801

(cherry picked from commit fef4948f172b66eaf8db520b381dd4a8237b5644)

forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc