Hi,

this one appears to be a rather simple case of missing diagnostic: in 
convert_to_void we aren't calling maybe_warn_nodiscard when we strip an 
INDIRECT_REF wrapping a CALL_EXPR thus we don't issue the diagnostic 
that we normally provide for plain CALL_EXPRs (eg, for a func returning 
a plain int). Tested x86_64-linux.

Thanks, Paolo.

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