[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:  new
        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):

 thanks Peter!  (merged it in)
 that solves one set of problems, next we need to understand why
 1) when i set --with-gcc=clang, the clang variant of the CPP flags isn't
 chosen
 2) while the cpp: foo, cpp-flags : blah info is printed in the configure
 script summary, it isn't substituted into the settings file!
 the CPP field is empty, and the CPP-Flags field @variableName@ isn't even
 substituted away. I suspect I'm not understanding how to use
 AC_SUBST([blah]) correctly

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8683#comment:9>
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