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

[GHC]

#8701: Update libffi-tarballs to latest libffi
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              Reporter:  lukexi      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  high        |        Milestone:  7.8.4
             Component:  Compiler    |          Version:  7.8.1-rc1
  (FFI)                              |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:  Building    |       Blocked By:
  GHC failed                         |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"39e206a7badd18792a7c8159cff732c63a9b19e7/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="39e206a7badd18792a7c8159cff732c63a9b19e7"
 Update libffi-tarballs submodule to libffi 3.1 (re #8701)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8701#comment:5>
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