gfortran.dg/gamma_(1|2).f90 fail on Darwin

[François-Xavier Coudert]

> Seems reasonable to me; but for the new test if "fortran_large_real"
> is "true" for systems with real(16): it will give the same failure
> since the exponent range is only 291. I think
> selected_real_kind (precision (0.0_8) + 1)
> is better.

It is, you're absolutely right. I intended to change it, but forgot.
Thanks for catching this!

FX