At some point, upstream SystemTap changed from using a
STAP_HAS_SEMAPHORES preprocessor variable for this, to using
_SDT_HAS_SEMAPHORES instead. We need to update our build system to
disable that as well.
The original discussion about use of semaphores is here:
https://bugzilla.gnome.org/show_bug.cgi?id=606044
This was breaking the build with -flto enabled, either because -flto
doesn’t work with semaphores.
https://bugzilla.gnome.org/show_bug.cgi?id=768198