The out-of-class definitions of the static constants are redundant if
the __cpp_inline_variables feature is supported, so use that macro to
decide whether to define them or not.
libstdc++-v3/ChangeLog:
* include/bits/regex.h: Check __cpp_inline_variables instead of
__cplusplus.
_AutomatonPtr _M_automaton;
};
-#if __cplusplus < 201703L
+#if ! __cpp_inline_variables
template<typename _Ch, typename _Tr>
constexpr regex_constants::syntax_option_type
basic_regex<_Ch, _Tr>::icase;