GCC 6.2 (I added it)

[coypu%SDF.ORG@localhost]

Hi!

I've added GCC 6.2.0 to pkgsrc, and the logic associated with it.
Overzealous packagers can now use GCC_REQD=6.2 to see even more build
failures!

A big change is that the default for C++ is -std=gnu++14, as opposed
to gnu++98. Another cause of fallout will likely be that we have
per-GCC-version rules in many cases.

(Similarly, less overzealous users who merely like Fortran can use:
PKGSRC_FORTRAN=gfortran and GFORTRAN_VERSION=6)

Have fun.