[GHC] #8683: add "cpp program" and "cpp program options" to settings file

[GHC]

#8683: add "cpp program" and "cpp program options" to settings file
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        Reporter:  carter            |            Owner:
            Type:  feature request   |           Status:  patch
        Priority:  normal            |        Milestone:  7.8.1
       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:  #8439
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Comment (by carter):

 OK, theres several things going on here, and i'm going to lay it out so i
 can be less confused (and hopefully i can understand your ideas better),
 and perhaps you can be less confused to! (though you are pointing out a
 real bug i think too)

 1) theres currently (and unfortunately), some places in the build system
 where GCC is hard coded.
    a) historically the only C compiler GHC would support was GCC. thus
 historically --with-gcc was just a way of picking which gcc to use system
 with more than one gcc installed (I think, i could be wrong here)
    b) the clang support for ghc is pretty recent, and theres definitely a
 few corners that still need cleanup

 the CPP mode for Haskell code is always "traditional mode", so the flags
 passed to haskell CPP != the flags passed to C, though there may be some
 overlap

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8683#comment:24>
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