Fix TLS for PIC systems

proc.c

@@ -75,6 +75,7 @@ ksegment(void)
   loadfsgs(SEG_KCPU << 3);
   
   // Initialize cpu-local variables.
+  c->tlsstruct = &c->tlsstruct;
   cpu = c;
   proc = 0;
 }

proc.h

@@ -59,6 +59,7 @@ struct cpu {
   int ncli;                    // Depth of pushcli nesting.
   int intena;                  // Were interrupts enabled before pushcli?
   void *tls[2];
+  void *tlsstruct;
 };
 
 extern struct cpu cpus[NCPU];