#826 Build fix for ambiguity with >= libc++ 17

include/date/date.h

@@ -4228,7 +4228,7 @@ inline
 std::basic_ostream<CharT, Traits>&
 operator<<(std::basic_ostream<CharT, Traits>& os, const local_time<Duration>& ut)
 {
-    return (os << sys_time<Duration>{ut.time_since_epoch()});
+    return (date::operator<<(os, sys_time<Duration>{ut.time_since_epoch()}));
 }
 
 namespace detail

include/date/ptz.h

@@ -667,7 +667,7 @@ time_zone::name() const
     auto print_offset = [](seconds off)
         {
             std::string nm;
-            hh_mm_ss<seconds> offset{-off};
+            date::hh_mm_ss<seconds> offset{-off};
             if (offset.is_negative())
                 nm += '-';
             nm += std::to_string(offset.hours().count());

include/date/tz.h

@@ -231,8 +231,8 @@ nonexistent_local_time::make_msg(local_time<Duration> tp, const local_info& i)
        << i.first.abbrev << " and\n"
        << local_seconds{i.second.begin.time_since_epoch()} + i.second.offset << ' '
        << i.second.abbrev
-       << " which are both equivalent to\n"
-       << i.first.end << " UTC";
+       << " which are both equivalent to\n";
+    date::operator<<(os, i.first.end) << " UTC";
     return os.str();
 }
 

include/date/tz_private.h

@@ -289,8 +289,7 @@ struct transition
     std::ostream&
     operator<<(std::ostream& os, const transition& t)
     {
-        using date::operator<<;
-        os << t.timepoint << "Z ";
+        date::operator<<(os, t.timepoint) << "Z ";
         if (t.info->offset >= std::chrono::seconds{0})
             os << '+';
         os << make_time(t.info->offset);