[GHC] #13237: Extend TH with addModCStub

[GHC]

#13237: Extend TH with addModCStub
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        Reporter:                    |                Owner:
  facundo.dominguez                  |  facundo.dominguez
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:  inline-c
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3106
       Wiki Page:                    |
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Comment (by nh2):

 I had an idea in mind on how we might do better for `addModCStub` than we
 can for `runIO`, but it depends on what GHC actually does with the C
 sources eventually (I don't know what it does):

 If GHC invokes a plain `gcc` or `cc` or `CC` or whatever, then all bets
 are off and we can't do better.

 But if it can separate the C preprocessor invocation and the C compiler
 invocation, then we could fully preprocess the C code (which expands all
 includes) and hash that into the interface file, allowing us to notice
 when included header files change.
 This is better than having to write that logic ourselves in TH based on
 `addDependentFile`, because one cannot in TH query what C preprocessor and
 flags GHC will invoke.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13237#comment:14>
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