* include/bits/regex.h (sub_match): Add noexcept to default
constructor and length observer.
(match_results): Add noexcept to default constructor and observers
with no preconditions. Define destructor as defaulted.
(operator==, operator!=, swap): Add noexcept.
(regex_iterator): Add default member initializers and define default
constructor and destructor as defaulted. Add noexcept to equality
and dereference operators.
From-SVN: r261266
