x86emul: force CLZERO feature flag in test harness

Commit b988e88cc0 ("x86/emul: Add feature check for clzero") added a
feature check to the emulator, which breaks the harness without this
flag being forced to true.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/tests/x86_emulator/x86_emulate.c
+++ b/tools/tests/x86_emulator/x86_emulate.c
@@ -89,6 +89,13 @@ int emul_test_cpuid(
         res->c |= 1U << 22;
     }
 
+    /*
+     * The emulator doesn't itself use CLZERO, so we can always run the
+     * respective test(s).
+     */
+    if ( leaf == 0x80000008 )
+        res->b |= 1U << 0;
+
     return X86EMUL_OKAY;
 }