GHC unnecessarily sign/zero-extends C call arguments

Ticket created following discussion in https://ghc.haskell.org/trac/ghc/ticket/7684#comment:58

It seems the zero/sign-extension that we're doing in the NCG for arguments less than a word in size is unnecessary, since the ABI doesn't specify any extension. There's some clarification of the spec in this thread: http://gcc.gnu.org/ml/gcc/2013-01/msg00448.html

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (NCG)
Test case
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CC	simonmar, tibbe
Operating system
Architecture