Remove the C++ flag for FreeBSD/OpenBSD targets
Remove the C++ flag for FreeBSD/OpenBSD targets

Building on FreeBSD and OpenBSD doesn't need linking against libstdc++
any more. With those gone, the C++ flag is unused.

kealist/ren-c,hostilefork/rebol,kealist/ren-c,codebybrett/ren-c,giuliolunati/ren-c,hostilefork/rebol,codebybrett/ren-c,kealist/ren-c,codebybrett/ren-c,giuliolunati/ren-c,rgchris/ren-c,mbk/ren-c,codebybrett/ren-c,hostilefork/rebol,rgchris/ren-c,draegtun/ren-c,kealist/ren-c,kealist/ren-c,hostilefork/rebol,draegtun/ren-c,giuliolunati/ren-c,draegtun/ren-c,hostilefork/rebol,codebybrett/ren-c,mbk/ren-c,giuliolunati/ren-c,mbk/ren-c,codebybrett/ren-c,kealist/ren-c,draegtun/ren-c,draegtun/ren-c,rgchris/ren-c,draegtun/ren-c,rgchris/ren-c,rgchris/ren-c,mbk/ren-c,hostilefork/rebol,giuliolunati/ren-c