[GHC] #12619: Allow users guide to be built independently from GHC

[GHC]

#12619: Allow users guide to be built independently from GHC
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        Reporter:  bgamari           |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 The only real sticky spot in this task is `utils/mkUserGuideParts`. It is
 a utility compiled by stage1 which takes a Haskell data structure
 containing bits of ReST and outputs ReST sources for the manpage and flags
 table. Ideally we would have a Sphinx extension to handle this but my
 previous attempts at this have been thwarted by various annoying technical
 limitations of Sphinx.

 The alternative would be to simply build `mkUserGuideParts` with the
 stage0 compiler (either by default or with a build system setting).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12619#comment:2>
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