Refactor std::basic_string_view members and add noexcept

Refactor std::basic_string_view members and add noexcept

	* include/bits/string_view.tcc (find_first_of, find_last_of)
	(find_first_not_of, find_last_not_of): Add noexcept.
	* include/std/string_view (basic_string_view(const _CharT*))
	(basic_string_view(const _CharT*, size_type))
	(front, back, remove_prefix, remove_suffix, find, rfind)
	(find_first_of, find_first_not_of): Add noexcept.
	(at(size_type), _S_compare(size_type, size_type)): Replace conditional
	expressions with if statements.
	(copy(_CharT*, size_type, size_type), substr(size_type, size_type)):
	Use _M_check for length checks.
	(compare(basic_string_view)): Reformat.
	(_M_check(size_type, const char)): Add noexcept(false).
	(_M_limit(size_type, size_type)): Use noexcept not _GLIBCXX_NOEXCEPT.

From-SVN: r254044