[GHC] #3353: Add CLDouble support

[GHC]

#3353: Add CLDouble support
---------------------------------+------------------------------------------
    Reporter:  igloo             |        Owner:              
        Type:  bug               |       Status:  new         
    Priority:  normal            |    Milestone:  _|_         
   Component:  Compiler          |      Version:  6.12.1      
    Keywords:                    |   Difficulty:  Unknown     
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
       Patch:  0                 |  
---------------------------------+------------------------------------------

Comment(by simonmar):

 Replying to [comment:7 igloo]:
 > `CLDouble` needs to be the same as the C `long double` type, so things
 don't go wrong when using the FFI with long doubles.

 Right, and adding a long double primitive type to GHC is not at all
 trivial.  I thought about doing an implementation in Haskell using the
 FFI, but that wouldn't work because the key thing you need to be able to
 do with a `CLDouble` is pass it to a foreign function, and for that we
 need support in the native code generator.  The primitives could be
 implemented using the FFI like we do for the 64-bit integral types on a
 32-bit platform (although that's not entirely satisfactory).

 As a workaround, code that needs `CLDouble` can go via a C wrapper that
 takes a `CLDouble *`.  Avoid manipulating `CLDouble` directly in Haskell,
 just talk in terms of pointers to `CLDouble`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3353#comment:8>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler