Log Message:
editors/emacs24: Fix build on DragonFly

I believe the segfault seen during building on DragonFly is a common one
seen by many platforms using GCC 5.x and later.  It's been fixed on Emacs
25 though.  Even though it's a generic GCC 5+ fix, limit it to DragonFly
only for now.  Taken from DPorts (from archives)