Use import list to hide new System.Exit.die

Soon, System.Exit will export the new `die` (see #9016) which would clash with
Cabal's own `die` implementation. This commit provides forward-compatiblity.

This also updates the Cabal submodule which requires a similiar fix.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Add System.Exit.die (re #9016)

The original proposal discussion can be found at

  http://thread.gmane.org/gmane.comp.lang.haskell.libraries/20872

Note this also updates the Haddock submodule to remove Hadock's local
`die` implementation.
Kill whitespace after cpp's `-I` flag

This clean-up is in a similiar spirit as 574ef4293b8676.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>