Add fixed branched thread creation example (closes #327)

Author: sim642

tests/regression/13-privatized/73-branched-thread-creation-priv2.c

@@ -0,0 +1,32 @@
+// PARAM: --enable ana.int.interval
+#include <pthread.h>
+#include <assert.h>
+
+int g = 1;
+pthread_mutex_t A = PTHREAD_MUTEX_INITIALIZER;
+
+void *t_fun(void *arg) {
+  return NULL;
+}
+
+int main(void) {
+  int x, r;
+  pthread_t id;
+
+  if (r) {
+    pthread_create(&id, NULL, t_fun, NULL);
+
+    pthread_mutex_lock(&A);
+    g = 5;
+    pthread_mutex_unlock(&A);
+  }
+  else {
+    g = 10;
+  }
+
+  pthread_mutex_lock(&A);
+  x = g; // may read 10!
+  assert(g <= 5); // UNKNOWN!
+  pthread_mutex_unlock(&A);
+  return 0;
+}