Default special members of regex types and add noexcept
* 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.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@261266 138bc75d-0d04-0410-961f-82ee72b054a4