Affected subclause: [stmt.return]
It is now invalid to return (explicitly or implicitly) from a function which is
declared to return a value without actually returning a value.
The caller and callee may assume fairly elaborate
return-value mechanisms for the return of class objects.
some flow paths execute a return without specifying any value,
the implementation must embody many more complications.
promising to return a value of a given type, and then not returning
such a value, has always been recognized to be a questionable
practice, tolerated only because very-old C had no distinction between
void functions and int functions.
Effect on original feature:
Deletion of semantically well-defined feature.
Difficulty of converting:
Add an appropriate return value to the source code, such as zero.
For several years, many existing C implementations have produced warnings in