added alias to tilde on french layouts for consistency

Linux TTY layer, and X11, have this key shifted produce tilde (~). This
change takes us from doing nothing to producing this in our TTY layer
(vt only, but sc is only special use today).

imp notes: Verified the above as best I could, and extracted the longer
commit message from the pull request messages.

Signed-off-by: Céleste Ornato <celeste@ornato.com>
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1688