Backport from mainline
2017-12-27 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/83600
* include/bits/regex.h (match_results::end()): Return valid iterator
when not ready.
* testsuite/28_regex/match_results/ctors/char/default.cc: Check that
unready objects are empty and have equal begin and end iterators.
* testsuite/28_regex/match_results/ctors/wchar_t/default.cc: Likewise.
From-SVN: r256292