Python: Add BasicBlockOrdering test

This one demonstrates a bug in the current CFG. In a dictionary
comprehension `{k: v for k, v in d.items()}`, we evaluate the value
before the key, which is incorrect. (A fix for this bug has been
implemented in a separate PR.)

Author: tausbn

python/ql/test/library-tests/ControlFlow/evaluation-order/BasicBlockOrdering.expected

@@ -0,0 +1 @@
+| test_comprehensions.py:21:29:21:40 | ControlFlowNode for BinaryExpr | Basic block ordering: $@ appears before $@ | test_comprehensions.py:21:35:21:35 | IntegerLiteral | timestamp 9 | test_comprehensions.py:21:21:21:21 | IntegerLiteral | timestamp 8 |

python/ql/test/library-tests/ControlFlow/evaluation-order/BasicBlockOrdering.ql

@@ -0,0 +1,20 @@
+/**
+ * Checks that within a single basic block, annotations appear in
+ * increasing minimum-timestamp order.
+ */
+
+import python
+import TimerUtils
+
+from TimerCfgNode a, TimerCfgNode b, int minA, int minB
+where
+  exists(BasicBlock bb, int i, int j |
+    a = bb.getNode(i) and b = bb.getNode(j) and i < j
+  ) and
+  minA = min(a.getATimestamp()) and
+  minB = min(b.getATimestamp()) and
+  minA >= minB
+select a,
+  "Basic block ordering: $@ appears before $@",
+  a.getTimestampExpr(minA), "timestamp " + minA,
+  b.getTimestampExpr(minB), "timestamp " + minB