Add example for unsoundness for calloc

Author: michael-schwarz

tests/regression/11-heap/12-calloc.c

@@ -0,0 +1,8 @@
+// PARAM: --set ana.malloc.unique_address_count 1
+#include<assert.h>
+#include<stdlib.h>
+int main() {
+  int* arr = calloc(5,sizeof(int));
+  arr[0] = 3;
+  assert(arr[2] == 0); //UNKNOWN
+}