algorithm: eliminate some redundant comparisons

This is only a minor optimization, but it's cleaner looking,
anyway. I figure it's worthwhile.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Makefile: switch from Python 2.6 to 2.7

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
genprime.pyx: Cython implementation added

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Makefile: add -lm for sqrt()

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
clang: fix build errors

They changed the CLI and I don't have time to figure out how. Let's just skip
the whole llc/opt/etc and go straight for a clang compile-and-link.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>