cad/openvsp: fix compilation in 10.1

The port broke on 10.1 since the update to gcc 4.9. Now we enforce
gcc 4.8 on FreeBSD 10.1.

PR: 215307
Submitted by: fernando.apesteguia@gmail.com (maintainer)
Approved by: mentors (implict)
MFH: 2016Q4