glibc: Explicitly disable msgfmt

If configure is rerun it finds msgfmt from gettext-native which is installed
during package_write_ipk|deb and means builds are not determinisic.

Whether msgfmt is needed is debatable (libc.mo files aren't generated without
it), however, we should at least be consistent which this patch ensures.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>