otherwise, infinite loops can result, as amply demonstrated by the new
configure (which duly replicated the old configures' behavior ...).
QMakeEvaluator::evaluateBuiltinExpand() now returns a VisitReturn like
all other evaluate*() functions. the string list return value is now an
out parameter; i used a reference instead of a pointer to avoid
adjusting 56 usages of it.
Task-number: QTBUG-13964
Change-Id: I51ca7df8d694c6ffe9d9899cba414b1b46f5ce95
Reviewed-by: Lars Knoll <lars.knoll@qt.io>