Added export def to test case.

test cases/common/6 linkshared/cpplib.cpp

@@ -1,3 +1,9 @@
-int cppfunc() {
+#if defined _WIN32
+    #define DLL_PUBLIC __declspec(dllexport)
+#else
+    #define DLL_PUBLIC __attribute__ ((visibility ("default")))
+#endif
+
+int DLL_PUBLIC cppfunc() {
     return 42;
 }