Another mtrace stub.

3514d335 · Silas Boyd-Wickizer · 2e5da953 · 3514d335
--- a/xv6-mtrace.h
+++ b/xv6-mtrace.h
@@ -20,4 +20,5 @@ char* strncpy(char *s, const char *t, int n);
 #else
 #define mtrace_lock_register(ip, x, name, op, y)
 #define mtrace_label_register(t, r, x, y, z, ip)
+#define mtrace_kstack_start(x, y)
 #endif