* gnu/services/avahi.scm, gnu/services/base.scm, gnu/services/databases.scm, gnu/services/dbus.scm, gnu/services/desktop.scm, gnu/services/dict.scm, gnu/services/mail.scm, gnu/services/networking.scm, gnu/services/sddm.scm, gnu/services/spice.scm, gnu/services/ssh.scm, gnu/services/web.scm, gnu/services/xorg.scm, gnu/system.scm: Replace the #~(string-append #$pkg "/bin/foo") idiom with (file-append pkg "/bin/foo").