Makefile: set LANG to workaround a MacOS X issue when dealing with UTF-8 files and sed.

If `LANG` is not set, this happens: `sed: RE error: illegal byte sequence`

Signed-off-by: Anil Madhavapeddy <anil@recoil.org>
Merge pull request #1 from avsm/master

Makefile: set LANG to workaround a MacOS X issue