[GHC] #8701: Update libffi-tarballs to latest libffi

[GHC]

#8701: Update libffi-tarballs to latest libffi
-------------------------------------+-------------------------------------
       Reporter:  lukexi             |             Owner:
           Type:  bug                |            Status:  new
       Priority:  high               |         Milestone:  7.8.1
      Component:  Compiler (FFI)     |           Version:  7.8.1-rc1
       Keywords:                     |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple   |   Type of failure:  Building GHC
     Difficulty:  Easy (less than 1  |  failed
  hour)                              |         Test Case:
     Blocked By:                     |          Blocking:
Related Tickets:                     |
-------------------------------------+-------------------------------------
 libffi 3.0.14 contains fixes necessary for successful iOS (and probably
 ARM in general) cross-compilation.

 I've created a new archive that can be dropped in to replace the current
 libffi-tarballs archive here:
 https://github.com/ghc-ios/libffi-
 tarballs/blob/master/libffi-3.0.14.tar.gz?raw=true

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8701>
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