This variable (a.k.a. rootlibexecdir), was exposed through the .pc file, but
not as rpm macro.
The .pc file must be located in the package that provides libraries, which
pulls in a lot of dependencies. In Fedora, the macros are split out to a
separate package so that other packages which need to refer to some systemd
path but don't otherwise require it, can only pull in the (much smaller and
dependency-less) macros package. zram-generator uses the path to specify the
location of systemd-makefs, so by using the rpm macro we'll be able to use
a much smaller buildroot.
# RPM macros for packages installing systemd unit files
+%_systemd_util_dir @rootlibexecdir@
%_unitdir @systemunitdir@
%_userunitdir @userunitdir@
%_presetdir @systempresetdir@