[GHC] #3879: Enable shared libraries on Windows

[GHC]

#3879: Enable shared libraries on Windows
---------------------------------+------------------------------------------
    Reporter:  igloo             |        Owner:  benl        
        Type:  feature request   |       Status:  new         
    Priority:  high              |    Milestone:  6.14.1      
   Component:  Compiler          |      Version:  6.12.1      
    Keywords:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
---------------------------------+------------------------------------------

Comment(by benl):

 I mean `#if !defined(mingw32_HOST_OS)`

 I recall that the problem with bootstrapping via-c was that without the
 import statement, no C-level prototype for this variable is emitted, and
 it's not imported via `Cmm.h`.

 If you add the above `#ifdef` and then try to boot the compiler via-c on
 windows it'll probably die. It'll still work with the NCG though. I don't
 have a better solution ATM.

 Note that `sm_mutex` is actually defined (for real) in `rts/sm/Storage.c`

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3879#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler