see https://bugs.gentoo.org/918937
from upstream https://git.sr.ht/~emersion/basu/commit/a08cf5a575325435040d35710dbac3d0c32b1676.patch
Drop unused symbols from version script
--- a/src/libsystemd/libsystemd.sym
+++ b/src/libsystemd/libsystemd.sym
@@ -72,9 +72,6 @@ global:
         sd_bus_get_current_message;
         sd_bus_get_current_handler;
         sd_bus_get_current_userdata;
-        sd_bus_attach_event;
-        sd_bus_detach_event;
-        sd_bus_get_event;
         sd_bus_add_filter;
         sd_bus_add_match;
         sd_bus_add_object;