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

[GHC]

#8683: add "cpp program" and "cpp program options" to settings file
-------------------------------------+------------------------------------
        Reporter:  carter            |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  highest           |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc2
      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):

 tl;dr

 the current state is such that if you do mix and match any combo of clang
 / gcc (and anything not them ) for with-gcc and with-cpp, you'll hit build
 failures because of how the libraries make files are setup.

 Also it currently doesn't have the right logic for CPPHS as an alternative
 to gcc/clang in the build side. BUT you can put that info in yourself in
 the settings file.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8683#comment:36>
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