[GHC] #10705: make configure warn when ghc-tarballs is missing on windows and provide guidance to download it.

[GHC]

#10705: make configure warn when ghc-tarballs is missing on windows and provide
guidance to download it.
-------------------------------------+-------------------------------------
        Reporter:  Phyx-             |                   Owner:
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Build System      |                 Version:  7.11
      Resolution:                    |                Keywords:
Operating System:  FreeBSD           |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #9218             |  Differential Revisions:  Phab:D1108
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Comment (by pgj):

 Replying to [comment:5 Phyx-]:
 > Whatever shell the freebsd one is using doesn't seem to like functions.

 By default, FreeBSD has the regular Bourne Shell (`/bin/sh`) from the base
 system, that shall support functions, I have used them a couple of times
 before.  However, the `function` keyword was not needed for that.
 Removing them from `configure.ac` fixes the problem for me.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10705#comment:6>
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