Default special members of regex types and add noexcept

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.

From-SVN: r261266