Add common optimized CRC32 function interface

patch as per https://github.com/MariaDB/server/pull/170 adds optimized Power8 implemention for CRC32-IEEE to complement existing CRC32C.

While I haven't included an implementation of an optimized CRC32-(IEEE) for intel, there is the following links that would enable this:

• http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-generic-polynomials-pclmulqdq-paper.pdf
• http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-paper.pdf
• http://web.archive.org/web/20140101100538/http://mail.madler.net/pipermail/zlib-devel_madler.net/2013-November/003096.html
• https://golang.org/src/hash/crc32/

Note the documentation mentions patents on CRC32 folding (which I haven't done).