[GHC] #8439: add a CPP program field to Settings file (decouple CPP program and C compiler choice)

[GHC]

#8439: add a CPP program field to Settings file (decouple CPP program and C
compiler choice)
-------------------------------------+------------------------------------
        Reporter:  carter            |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.10.1
       Component:  Compiler          |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #8683
-------------------------------------+------------------------------------
Changes (by hvr):

 * related:   => #8683


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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8439#comment:1>
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