implement proper type promotion in compilation of C calls

> 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#.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
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