blake: rewrite the cache system

Unlike other hash algos, blake256 compute the hash
with blocks of 64 bytes.

We can do the first part on the cpu, only the 4 last int32
are computed on gpu (including the tested nonce)

Previous method was also using this kind of cache with a crc.

Blake Hash Speed: +5%
linux: tune cflags, no binary releases

unlike mingw, linux binaries are self-built,
so we can use the flag -march=native

+ remove some unused vars