PR libstdc++/63920
	* include/bits/regex_executor.h: Make _M_begin non const.
	* include/bits/regex_executor.tcc (_Executor<>::_M_search): Increase
	_M_begin in search algorithm, so that _M_begin is treated as
	"current start position" for each search iteration.
	* testsuite/28_regex/algorithms/regex_search/ecma/flags.cc: New
	testcase.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@218037 138bc75d-0d04-0410-961f-82ee72b054a4