PR libstdc++/68863
	* include/bits/regex_executor.tcc (_Executor::_M_lookahead):
	Copy the captured content for lookahead, so that the backreferences
	inside can refer to them.
	* testsuite/28_regex/algorithms/regex_match/ecma/char/68863.cc:
	New testcase.

From-SVN: r231641