[GHC] #8723: sdist should not have to build everything

[GHC]

#8723: sdist should not have to build everything
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        Reporter:  nomeata           |                   Owner:
            Type:  task              |                  Status:  patch
        Priority:  low               |               Milestone:  7.12.1
       Component:  Build System      |                 Version:  7.6.3
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:  Phab:D917
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Comment (by thomie):

 How about adding `happy` and `alex` to the build requirements for building
 from source tarballs?

 Then generating a source tarball becomes easier.

 As suggested by SPJ in ticket:1693#comment:25.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8723#comment:3>
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