benchtests: Add more coverage for strcmp and strncmp benchmarks

Add more small and medium sized tests for strcmp and strncmp.

As well for strcmp add option for more direct control of
alignment. Previously alignment was being pushed to the end of the
page. While this is the most difficult case to implement, it is far
from the common case and so shouldn't be the only benchmark.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>