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

unsupported/test/cxx11_tensor_custom_index.cpp

@@ -88,7 +88,7 @@ static void test_sizes_as_index()
 }
 
 
-void test_cxx11_tensor_custom_index() {
+EIGEN_DECLARE_TEST(cxx11_tensor_custom_index) {
   test_map_as_index<ColMajor>();
   test_map_as_index<RowMajor>();
   test_matrix_as_index<ColMajor>();