[GHC] #15254: Cabal submodule bump is needed

[GHC]

#15254: Cabal submodule bump is needed
-------------------------------------+-------------------------------------
           Reporter:                 |             Owner:  (none)
  quasicomputational                 |
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.5
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Cabal HEAD has recently been somewhat broken
 (https://github.com/haskell/cabal/issues/5318) and the current submodule
 is pointing to a buggy commit. This only manifests when installing `build-
 type: Custom` packages, because that uses the bad code from the bootstrap
 Cabal; `build-type: Simple` will use good code from the external `cabal-
 install` process.

 Please bump the Cabal submodule to fix this. I've verified that the
 observed problem (`happy` breaking) goes away when this is done.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15254>
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