[GHC] #9703: Add missing calling conventions to Template Haskell

[GHC]

#9703: Add missing calling conventions to Template Haskell
-------------------------------------+-------------------------------------
       Reporter:  luite              |                   Owner:  ekmett
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Core Libraries     |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Easy (less than 1  |         Type of failure:
  hour)                              |  None/Unknown
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 Template Haskell only supports the `CCall` and `StdCall` calling
 conventions, while GHC supports more:

 http://git.haskell.org/packages/template-
 haskell.git/blob/9bcc122819a6f4a2ae7ad569717324b8368e801c:/Language/Haskell/TH/Syntax.hs#l1311

 http://git.haskell.org/ghc.git/blob/7369d2595a8cceebe457a44c8400828f4df87ea0:/compiler/prelude/ForeignCall.lhs#l159

 `CApiConv`, `PrimCallConv` and `JavaScriptCallConv` are missing, and I
 think they should just be added unless this is expected to lead to
 problems.

 I'd personally like to have `JavaScriptCallConv` so I can remove the
 horrible hacks to make ghcjs-ffiqq (https://github.com/ghcjs/ghcjs-ffiqq)
 work. I imagine that `PrimCallConv` would be useful for a package using a
 similar approach for high performance inline assembly or LLVM with
 quasiquotes.

 A small change in GHC required to convert the new constructors, and
 possibly to check if the required extension is enabled.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9703>
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