unwind: Don't fail completely if fingerprinting fails

The fingerprinting code is rather fragile and fingerprints are not
essential. If generating fingerprints fails, continue without them.

Partially fixes #81.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Signed-off-by: Richard Marko <rmarko@redhat.com>
Disable fingerprinting on arches other than x86_64

The code that does fingerprinting currently only supports x86_64 (and
though i386 support should not be difficult to add, it has low
priority). The architecture is detected at build time and fingerprinting
enabled only for x86_64.

Closes #81.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Signed-off-by: Richard Marko <rmarko@redhat.com>