Gfortran and Fortran 2018 standard enforcement

GCC 8 includes Gfortran 8, which adds -std=f2018 option, which is a good start on enforcing/allowing Fortran 2018 standard. Gfortran 8 can be obtained from the Ubuntu-test PPA. Note that libraries such as HDF5 etc. will have to be recompiled to work with Gfortran 8.1 due to the new version 5 ABI.

Gfortran 8 can be used to do a rough check of Fortran 2018 standard correctness for commonly uses syntax.

Gfortran 9 is already under development, with ever increasing modern Fortran 20082018 standard compliance.