Clarify sequencing of std::unexpected and lifetime of function arguments

Clause / Subclause / Annex: 
15.4
Para/Table/Figure: 
8
Comment type: 
Te
Comment / justification for change: 

Unclear if std::unexpected is called before or after the function arguments have been destroyed

Recommended change: 

Clarify the sequence of calling unexpected with respect to interesting objects, such as function arguments or partially constructed bases and members when called from a constructor or destructor

MB: 
UK