[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 trommler):

 Replying to [comment:22 carter]:
 > @trommler, hrmmmm
 >
 > I was doing the command + flag design because that maps to the current
 GHC dynflags model,
 ... and I tried to set {{{gcc -E}}} for cpp and failed. GHC tries to exec
 {{{gcc -E}}} then and that does not exist. We could fix that by parsing
 CPP in configure (once) or in GHC (at every invocation)
 or stick with your original design (which I did for now in my branch).
 >
 > perhaps it'd be better to have distinct CPP programs for C and Haskell
 in the build model?
 I think, yes.

 I don't fully understand what {{{--with-gcc}}} is supposed to do. It
 changes the C compiler half way through configure and then even sets
 {{{CC}}}. The wiki says it specified the compiler used to compile C files
 but GHC will use its own C compiler. To me that sounds like we should
 actually set the C compiler using {{{CC=<C compiler>}}} on the configure
 command line. But I might be missing a major issue here.
 > Does this mean they should be disjoint in GHC's dynflags too?
 Do you mean there should be another set of CPP and CPPFLAGS for C files? I
 don't think so.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8683#comment:23>
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