After some 19 months of deprecation, mark this port for expiration in
two months (end of October 2019).

GCC 5 went end-of-life upstream in October 2017, so this port is now
scheduled for removal more than two years after that. Nothing in
the Ports Collection depends on it any longer (and has not for a
while), and the default version of GCC in the ports tree is GCC 9,
four major releases later.

While here stll create a proper USES block in the Makefile. [1]

Reported by: portlint [1]