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This turned out not to be too hard, just a matter of figuring out the
correct argument list size by peeking inside FunPtr's type argument,
and in the C backend we have to emit an appropriate prototype for the label.

Needed in lieu of -XRelaxedPolyRec

  
Previously we declared all external labels with type StgWord[],
because the same label might be used at different types in the same
file, e.g. if there are multiple foreign import declarations for the
same function.  However, we have to declare called functions with the
right type on Windows, because this is the only way to make the
compiler add the appropriate '@n' suffix for stdcall functions.

Related to this is the reason we were getting mangler complaints
(epilogue mangling) when compiling the RTS with -fvia-C.  The function
barf() doesn't return, but we had lost that information by declaring
our own prototypes, and so gcc was generating extra code after the
call to barf().

For more details see
http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/PprC

C-- no longer has 'hints'; to guide parameter passing, it
has 'kinds'.  Renamed type constructor, data constructor, and record
fields accordingly

This version combines forward/backard into a type class
(actually two classes) of analysis and transformation.
These type classes will always be expanded away at the client,
so SLPJ may wonder why they exist: it is because the interface
to this module is already very broad, and by overloading the functions 
for forward and backward problems, we cut the cognitive load on the
clients in half.

Nothing too deep here; primarily tinking with prettyprinting
and names.  Also eliminated some warnings.  This patch covers
most (but not all) of the code NR changed at the very end
of September 2007, just before ICFP hit...

This has several advantages:

 - -fvia-C is consistent with -fasm with respect to FFI declarations:
   both bind to the ABI, not the API.

 - foreign calls can now be inlined freely across module boundaries, since
   a header file is not required when compiling the call.

 - bootstrapping via C will be more reliable, because this difference
   in behavour between the two backends has been removed.

There is one disadvantage:

 - we get no checking by the C compiler that the FFI declaration
   is correct.

So now, the c-includes field in a .cabal file is always ignored by
GHC, as are header files specified in an FFI declaration.  This was
previously the case only for -fasm compilations, now it is also the
case for -fvia-C too.

Modules that need it import it themselves instead.

re-recording to avoid new conflicts was too hard, so I just put it
all in one big patch :-(  (besides, some of the changes depended on
each other.)  Here are what the component patches were:

Fri Dec 28 11:02:55 EST 2007  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * document BreakArray better

Fri Dec 28 11:39:22 EST 2007  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * properly ifdef BreakArray for GHCI

Fri Jan  4 13:50:41 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * change ifs on __GLASGOW_HASKELL__ to account for... (#1405)
  for it not being defined. I assume it being undefined implies
  a compiler with relatively modern libraries but without most
  unportable glasgow extensions.

Fri Jan  4 14:21:21 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * MyEither-->EitherString to allow Haskell98 instance

Fri Jan  4 16:13:29 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * re-portabilize Pretty, and corresponding changes

Fri Jan  4 17:19:55 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * Augment FastTypes to be much more complete

Fri Jan  4 20:14:19 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * use FastFunctions, cleanup FastString slightly

Fri Jan  4 21:00:22 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * Massive de-"#", mostly Int# --> FastInt (#1405)

Fri Jan  4 21:02:49 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * miscellaneous unnecessary-extension-removal

Sat Jan  5 19:30:13 EST 2008  Isaac Dupree <id@isaac.cedarswampstudios.org>
  * add FastFunctions

This allows the instance of UserOfLocalRegs to be within Haskell98, and IMHO
 makes the code a little cleaner generally.
This is one small (though tedious) step towards making GHC's code more
 portable...

was instance Outputable CmmGraph
type CmmGraph = LGraph Middle Last
now instance (ctx) => Outputable (LGraph m l),
in module with LGraph where it belongs
This also let us reduce the context of DebugNodes to Haskell98,
leaving that class's only extension being multi-parameter.
(also Outputable (LGraph M Last) with M = ExtendWithSpills Middle
was another redundant instance that was then removed)

UserOfLocalRegs (ZLast Last) isn't Haskell98, but it was just as
good an instance to be UserOfLocalRegs a => UserOfLocalRegs (ZLast a)

cmmMiniInline counts the uses of local variables, so it can easily
eliminate assigments to unused locals.  This almost never gets
triggered, as we don't generate any dead assignments, but it will be
needed by a forthcoming cleanup in CgUtils.emitSwitch.