[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:  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):

 just rebased it

 (I think i did the rebase correctly, but I have no clueeee)

 theres two parts to this patch
 1) making ghc have its CPP settable / configable in the settings file.
 This seems work
 2) allowing ghc to be built with different CC and CPP. this doesn't quite
 work, but it does allow use to set it explicitly, and initializes the
 right fields in settings, but theres CPP stuff lying all around the build
 system that i'm still unfamiliar with and haven't been address here.

 this also add --with-cpp and --with-cpp-flags flags to configure

 currently for building things,  -with-cpp and with-gcc need to point to
 the same program or various bugs in the build system start creeping up!
 It also seems to have surfaced at least one new race condition in the
 build system. I will try to dig into that more later.

 What i also need to finally test properly is if the resulting ghc can
 handle its settings file being pointed to cpphs

 Also i thought i had added logic to handle cpphs as a cpp option, but it
 looks like i lost track of that commit

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8683#comment:32>
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