cmake: fix systemd user unit install path

Installing to ${CMAKE_INSTALL_LIBDIR}/systemd/user can end up in
/usr/lib64/systemd/user on multilib systems, which systemd does not
search. Use pkg-config's systemduserunitdir instead (with a fallback
to /usr/lib/systemd/user) so the unit is always installed in the
correct location.

Author: peppapig450

CMakeLists.txt

@@ -140,4 +140,10 @@ endif()
 include(GNUInstallDirs)
 
 install(TARGETS hyprsunset)
-install(FILES ${CMAKE_BINARY_DIR}/systemd/hyprsunset.service DESTINATION ${CMAKE_INSTALL_LIBDIR}/systemd/user)
+
+pkg_get_variable(SYSTEMD_USER_UNIT_DIR systemd systemduserunitdir)
+if (NOT SYSTEMD_USER_UNIT_DIR)
+  set(SYSTEMD_USER_UNIT_DIR "${CMAKE_INSTALL_PREFIX}/lib/systemd/user")
+endif()
+
+install(FILES ${CMAKE_BINARY_DIR}/systemd/hyprsunset.service DESTINATION "${SYSTEMD_USER_UNIT_DIR}")