PR libstdc++/61424
* include/bits/regex.tcc (__regex_algo_impl<>): Use DFS for ECMAScript,
not just regex containing back-references.
* include/bits/regex_compiler.tcc (_Compiler<>::_M_disjunction):
exchange _M_next and _M_alt for alternative operator,
making matching from left to right.
* include/bits/regex_executor.h (_State_info<>::_M_get_sol_pos):
Add position tracking fom DFS.
* include/bits/regex_executor.tcc (_Executor<>::_M_main_dispatch,
_Executor<>::_M_dfs): Likewise.
* include/bits/regex_scanner.h: Remove unused enum entry.
* testsuite/28_regex/algorithms/regex_search/61424.cc: New
testcase from PR.
From-SVN: r212184
