Log Message:
hunspell: bump required GCC to 7, and use c++11.

This is required to get this to build on NetBSD/i386 8.0 and
NetBSD/macppc 8.0, where the in-tree c++ compiler has apparently
now become too old.  Bump to c++11 based on configure tests, which
among other things checks if c++11 is enabled by default.
Bump PKGREVISION.