volk: fixing QA to address bugs 582, 583, and 627

582 and 583 are probably compiler bugs, and an upstream bug has been filed
on launchpad with Linaro GCC. A static cast of the tolerance is not happening
on armhf architectures. The work around forces a cast by using the values
immediately after assignment.

627 is addressed by adding a fabs call when checking if a number is close to 0.
In this case we also make sure the other buffer is within tolerance.
volk: use volk_malloc to create buffers in QA