Since makekeys is built using build environment's gcc and
runs natively, we have to make sure that the size of the
Signature type is the same on both the native environment
and the target, otherwise we get mismatches upon running X,
and some LSB test failures (xts5).

Use an unsigned 32-bit integer on all platforms. Also,
eliminate the redundant multiple typedefs for the
Signature type.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>