Fix build under gfortran7
Bug 222560: comms/wspr: fails to build with lang/gcc7 or later
Reported by: Jan Beich <jbeich@FreeBSD.org>
WSPR (pronounced "whisper") stands for "Weak Signal Propagation Reporter."
This program is designed for sending and receiving low-power transmissions
to test propagation paths on the MF and HF bands. Users with internet access
can watch results in real time at WSPRnet.