Experimental Fortran 2018 compiler (20171201)

This release is based on the Sourcery Institute GCC fork's teams branch with commits from the GCC git mirror through 28 November 2017 and commits unique to the teams branch through 1 December 2017. With the additional support this branch provides for teams, gfortran is approaching full Fortran 2018 compliance, notwithstanding bugs, some partially supported major features, and a few unsupported minor features. "Fortran 2018" is the new name adopted by the Fortran standards committee for what was formerly known as "Fortran 2015," the most recent definition of which is defined in a July 2017 committee draft.