[eigen] NoChange_t, Sequential_t, etc.

[Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>]

Hi guys,

are there any objections of removing the global variables

struct Sequential_t {};
namespace {
  EIGEN_UNUSED Sequential_t Sequential;
}

and replacing them by

struct Sequential {};

I started using Eigen with the Intel compiler and I am getting many
warnings regarding unused variables and there is no easy way to remove
those.

I am quite sure, the "trick" above is anyways a remnant from C which
should not be required anymore. If it is still needed we could at
least typedef define the structs.

Regards,
Hauke