comms/wsjtx: Give bin/jt9 an executable stack

jt9 is supposed to have an executable stack, but a bug in lld (now
fixed upstream) prevents that.

This change explicitly sets the required exectuable stack for jt9.
Much simpler than using mprotect et. al.

PR: 278939
Reported by: jeffpc@josefsipek.net
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D48572