IMPORT: slz: support crc32c for lookup hash on sse4 but only if requested

IMPORT: slz: support crc32c for lookup hash on sse4 but only if requested

If building for sse4 and USE_CRC32C_HASH is defined, then we can use
crc32c to calculate the lookup hash. By default we don't do it because
even on skylake it's slower than the current hash, which only involves
a short multiply (~5% slower). But the gains are marginal (0.3%).

This is slz upstream commit 44ae4f3f85eb275adba5844d067d281e727d8850.

Note: this is not used by default and only merged in order to avoid
divergence between the code bases.