preprocessor: add an example of a macro that generates code

Change-Id: I902ebd73e039b8c3f44eca456be87809d1e1d3a4
Reviewed-by: hjk <qthjk@ovi.com>

tests/auto/cplusplus/preprocessor/data/macro_expand_1.cpp

+#define DECLARE_CLASS(s) class s
+DECLARE_CLASS(QString);

tests/auto/cplusplus/preprocessor/data/macro_expand_1.out.cpp

+# 1 "data/macro_expand_1.cpp"
+#gen true
+# 1 "data/macro_expand_1.cpp"
+class
+#gen false
+# 2 "data/macro_expand_1.cpp"
+              QString;

tests/auto/cplusplus/preprocessor/tst_preprocessor.cpp

@@ -677,6 +677,8 @@ void tst_Preprocessor::comparisons_data()
         << "macro_pounder_fn.c" << "" << "";
     QTest::newRow("macro_expand")
         << "macro_expand.c" << "macro_expand.out.c" << "";
+    QTest::newRow("macro_expand_1")
+        << "macro_expand_1.cpp" << "macro_expand_1.out.cpp" << "";
     QTest::newRow("macro-test")
         << "macro-test.cpp" << "macro-test.out.cpp" << "";
     QTest::newRow("empty-macro")