Handle unlikely errors from personality syscall

Despite being marked as SYSCALL_NEVER_FAILS, personality syscall still
might report a failure on some architectures due to obscure kernel
bugs.  Check for this unlikely case and let users know that their
kernel has gone bananas.

* personality.c (SYS_FUNC(personality)): Do not parse syscall return
value in case of syserror.

personality.c

@@ -50,6 +50,9 @@ SYS_FUNC(personality)
 		return 0;
 	}
 
+	if (syserror(tcp))
+		return 0;
+
 	pers = tcp->u_rval;
 	const char *type = xlookup(personality_types, pers & PER_MASK);
 	char *p;