xen/ubsan: Fix UB in type_descriptor declaration

struct type_descriptor is arranged with a NUL terminated string following the
kind/info fields.

The only reason this doesn't trip UBSAN detection itself (on more modern
compilers at least) is because struct type_descriptor is only referenced in
suppressed regions.

Switch the declaration to be a real flexible member.  No functional change.

Fixes: 00fcf4d ("xen/ubsan: Import ubsan implementation from Linux 4.13")
Signed-off-by: Andrew Cooper <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>
Release-Acked-by: Oleksii Kurochko <[email protected]>

xen/common/ubsan/ubsan.h

@@ -10,7 +10,7 @@ enum {
 struct type_descriptor {
 	u16 type_kind;
 	u16 type_info;
-	char type_name[1];
+	char type_name[];
 };
 
 struct source_location {