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

[Richard Henderson]

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


r~