re PR libstdc++/70745 (Wrong handling of regex_constant::match_not_eow and regex_constant::match_not_bow)

	PR libstdc++/70745
	* include/bits/regex_executor.tcc (_Executor<>::_M_word_boundary):
	Fix the match_not_bow and match_not_eow behavior.
	* testsuite/28_regex/regression.cc: Add testcase.

From-SVN: r235382