implement proper type promotion in compilation of C calls

[igloo]

> commit 229323898b0809047b19b79c181085430cce9850
> Author: Ian Lynagh <ian@well-typed.com>
> Date:   Thu Nov 1 14:13:05 2012 +0000
>
>      Fix popcnt calls
>
>      We don't want to narrow the argument size before making the foreign
>      call: Word8 still gets passed as a Word-sized argument

I'm not sure this is right (I added the narrowing, FWIW).  The fact that
Word8 gets promoted to Word is part of the C ABI, and we don't want to
do that when popcnt is being implemented directly by the native codegen.
  I know it is currently broken on some platforms, but I think the fix
is to implement the proper type promotion in the compilation of C calls.

A useful test for this is cgrun071. If we get it wrong then it fails on x86, as the stack alignment is wrong when calling e.g. popCnt8#.

[tibbe]

cgrun071 now segfaults. See linked ticket.

[simonmar]

Please try the attached patch. It validates for me on x86-64/Linux, but I don't think it affects anything there.

[marlowsd@…]

commit 085e8145f63c8f42d8bc19cd3cff52b8cd5b6455

Author: Simon Marlow <marlowsd@gmail.com>
Date:   Wed Feb 20 11:43:33 2013 +0000

    x86: promote arguments to C functions according to the ABI (#7383)
    
    I don't think the x86-64 version is quite right, but this ought to be
    enough to pass cgrun071.
    
    This code is terrible and needs a complete refactor.  There's a lot of
    duplication, and we ought to be specifying the ABI in a much more
    abstract way (like LLVM).

 compiler/nativeGen/X86/CodeGen.hs |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)

[igloo]

cgrun071 passes on OS X x86. I've pushed it.