[libiberty] Add ARG_UNUSED as a C++-friendly replacement for ATTRIBUTE_UNUSED

[Bernardo Innocenti]

Richard Henderson wrote:
> On Tue, Jul 13, 2004 at 09:50:36AM +0200, Bernardo Innocenti wrote:
> 
>>define ARG_UNUSED(T,N) to "T N").
> 
> 
> If we do this, I'd prefer
> 
> 	T ARG_UNUSED(N)
> 
> #ifdef __cplusplus
> # define ARG_UNUSED(N)
> #elif somegccversion
> # define ARG_UNUSED(N)	N ATTRIBUTE_UNUSED
> #else
> # define ARG_UNUSED(N)	N
> #endif

This wouldn't allow us to support g++ < 3.4:

 # define ARG_UNUSED(T,N)   ATTRIBUTE_UNUSED T N

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
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