fix allocate/free size mismatch in interpret.cpp

This was causing a crash every time the VM was run when build using
mode=debug and process=interpret.

src/interpret.cpp

@@ -3166,7 +3166,7 @@ class MyProcessor: public Processor {
   }
 
   virtual void dispose(vm::Thread* t) {
-    t->m->heap->free(t, sizeof(Thread));
+    t->m->heap->free(t, sizeof(Thread) + t->m->stackSizeInBytes);
   }
 
   virtual void dispose() {

src/posix.cpp

@@ -904,6 +904,7 @@ class MySystem: public System {
   }
 
   virtual void abort() {
+    *static_cast<void**>(0) = 0;
     ::abort();
   }