Add test where address containing unknown should escape known

Author: sim642

tests/regression/02-base/70-escape-unknown.c

@@ -0,0 +1,28 @@
+#include <pthread.h>
+#include <assert.h>
+
+int *p;
+
+void *t_fun(void *arg) {
+  if (arg != NULL) {
+    *((int*)arg) = 42;
+  }
+  return NULL;
+}
+
+int main() {
+  pthread_t id, id2;
+  int *r; // unknown
+  int i = 5;
+
+  pthread_create(&id, NULL, t_fun, NULL); // enter multithreaded
+
+  p = r;
+  p = &i;
+
+  pthread_create(&id2, NULL, t_fun, p); // i should escape, even if p contains unknown
+
+  assert(i == 5); // UNKNOWN!
+
+  return 0;
+}