Bump PORTREVISION for ports depending on the canonical version of GCC
defined via Mk/bsd.default-versions.mk which has moved from GCC 7.4 t
GCC 8.2 under most circumstances.

This includes ports

• with USE_GCC=yes or USE_GCC=any,
• with USES=fortran,
• using Mk/bsd.octave.mk which in turn features USES=fortran, and
• with USES=compiler specifying openmp, nestedfct, c11, c++0x, c++11-lang, c++11-lib, c++14-lang, c++17-lang, or gcc-c++11-lib

plus, as a double check, everything INDEX-11 showed depending on lang/gcc7.

PR: 231590