C++: Add a generated file to the test.

Author: geoffw0

cpp/ql/test/query-tests/Summary/LinesOfCode.expected

@@ -1 +1 @@
-| 93 |
+| 96 |

cpp/ql/test/query-tests/Summary/generated-file.cpp

@@ -0,0 +1,12 @@
+/**
+ * This file is generated by abc.xyz.  Do not edit!
+ *
+ * (except that this isn't really a generated file, but the above is the typical sort of comment
+ *  you see at the beginning of a true generated file).
+ */
+
+int generated_function() {
+	// ...
+
+	return 1;
+}