Fix old python2 test issue.

The map function returns a list in python2, but not in python3.
Force the test in cpp.py get_blocks() function to return a list.

Test: All cpp.py unit tests pass.
Change-Id: I1a63b92ac6cdb785830846fbd7e726eca7520e96

libc/kernel/tools/cpp.py

@@ -1647,7 +1647,7 @@ class BlockParserTests(unittest.TestCase):
 
     def get_blocks(self, lines):
         blocks = BlockParser().parse(CppStringTokenizer('\n'.join(lines)))
-        return map(lambda a: str(a), blocks)
+        return list(map(lambda a: str(a), blocks))
 
     def test_hash(self):
         self.assertEqual(self.get_blocks(["#error hello"]), ["#error hello"])