C++: Move codegen test into the CppTools plugin.

Change-Id: I4c70a9dbd5445188c3d202427da96e1c6ff90b63
Reviewed-by: Bill King <bill.king@nokia.com>

src/plugins/cpptools/cpptools.pro

@@ -67,3 +67,8 @@ SOURCES += completionsettingspage.cpp \
 FORMS += completionsettingspage.ui \
     cppfilesettingspage.ui \
     cppcodestylesettingspage.ui
+
+equals(TEST, 1) {
+    SOURCES += \
+        cppcodegen_test.cpp
+}