dbus: Add libsm dependency (fix for issue #18267) (#18268)

dbus has a dependency on libSM which was not being declared (and would
normally be satisfied by using system libraries).

var/spack/repos/builtin/packages/dbus/package.py

@@ -30,6 +30,7 @@ class Dbus(Package):
     depends_on('pkgconfig', type='build')
     depends_on('expat')
     depends_on('glib')
+    depends_on('libsm')
 
     def install(self, spec, prefix):
         configure(