x86/shadow: drop callback_mask pseudo-variables

x86/shadow: drop callback_mask pseudo-variables

In commit 90629587e16e ("x86/shadow: replace stale literal numbers in
hash_{vcpu,domain}_foreach()") I had to work around Clang not following
gcc in certain relaxed requirements as to the expressions usable with
_Static_assert() (gcc tolerates static const variables in otherwise
integer constant expressions). Roberto suggests that we'd better not
rely on such behavior. Drop the involved static const-s, using their
"expansions" in both of the prior use sites each. This then allows
dropping the short-circuiting of the check for clang.

Requested-by: Roberto Bagnara <roberto.bagnara@bugseng.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>