Use __attribute__((target(sse4.2))) for SSE42 CRC32C

[Devulapalli, Raghuveer]

Based on the discussion in PostgreSQL: Re: Proposal for Updating CRC32C with 
AVX-512 
Algorithm.<https://www.postgresql.org/message-id/ZyziAXhsgfqakSI4%40nathan>, 
this patch leverages pg_attribute_target to build the SSE42 CRC32C code using 
function attributes.

Raghuveer

v1-0001-Use-__attribute__-target-sse4.2-for-SSE42-CRC32C.patch
Description: v1-0001-Use-__attribute__-target-sse4.2-for-SSE42-CRC32C.patch