No diagnostic for checking reqd_work_group_size and max_work_group_size attributes when merging

[smanna12]

//FIXME: We do not have support yet for checking
// reqd_work_group_size and max_work_group_size
// attributes when merging, so the test compiles without
// any diagnostic when it shouldn't.
[[sycl::reqd_work_group_size(64, 64, 64)]] void f12();
[[intel::max_work_group_size(16, 16, 16)]] void f12(); // expected error but now OK.