Don't name something exit().

On aarch64 due to some terrifying include chain we wind up with
Cryptlib's definition of exit here.  I'm not a glutton for punishment,
so I'm just changing the name so it's not coliding.

Signed-off-by: Peter Jones <pjones@redhat.com>
Make sure we don't try to load a binary from a different arch.

Since in theory you could, for example, get an x86_64 binary signed that
also behaves as an ARM executable, we should be checking this before
people build on other architectures.

Signed-off-by: Peter Jones <pjones@redhat.com>