1. put the definitions of variables long_shifts and short_shifts and
function shift_crc() in #ifndef _TD_ARM_, because this function and
these variables are not used/called for arm64 build in travis. Hence
warnings come up as errors.
2. Added arm64 jobs into .travis.yml by adding -DCPUTYPE=aarch64 with
cmake command.
Signed-off-by: Nodidev <odidev@puresoftware.com>