x86/guest: fix build when HVM and !PV32

The commit referenced below still wasn't careful enough - with COMPAT we
will have a compat_handle_okay() visible already, which we first need to
get rid of.

Fixes: bd1e7b47ba ("x86/shim: fix build when !PV32")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

xen/arch/x86/pv/shim.c

@@ -679,6 +679,7 @@ void pv_shim_inject_evtchn(unsigned int port)
 # include <compat/grant_table.h>
 #else
 # define compat_gnttab_setup_table gnttab_setup_table
+# undef compat_handle_okay
 # define compat_handle_okay guest_handle_okay
 #endif