PR libstdc++/64302

	PR libstdc++/64302
	PR libstdc++/64303
	* include/bits/regex.h (match_results::cbegin, match_results::cend,
	regex_token_iterator::regex_token_iterator,
	regex_token_iterator::_M_normalize_result): Fix match_results cbegin
	and cend and regex_token_iterator::_M_result invariant.
	* include/bits/regex.tcc: Fix regex_token_iterator::_M_result invariant.
	* testsuite/28_regex/iterators/regex_token_iterator/64303.cc: Testcase.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@218810 138bc75d-0d04-0410-961f-82ee72b054a4