Get rid of EIGEN_TEST_FUNC, unit tests must now be declared with EIGEN_DECLARE_TEST(mytest) { /* code */ }.

This provide several advantages:
- more flexibility in designing unit tests
- unit tests can be glued to speed up compilation
- unit tests are compiled with same predefined macros, which is a requirement for zapcc

test/dense_storage.cpp

@@ -52,7 +52,7 @@ void dense_storage_assignment()
     VERIFY_IS_EQUAL(raw_reference[i], raw_copied_reference[i]);
 }
 
-void test_dense_storage()
+EIGEN_DECLARE_TEST(dense_storage)
 {
   dense_storage_copy<int,Dynamic,Dynamic>();  
   dense_storage_copy<int,Dynamic,3>();