Checksum performance is slow on Arm64

The checksum performance in folly is not optimized on Arm64 with Neon, which induce that the performance is quite slow.

./folly/hash/detail/ChecksumDetail.h

Cachelib heavily rely on Folly to realize the checksum.

From the perf top, in the cachelib with hyprid cache configuration, the checksum is consuming a lot of CPU time, which has been a bottleneck.
```
Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz
$ checksum_benchmark --bm_min_usec=10000
============================================================================
folly/hash/test/ChecksumBenchmark.cpp relative time/iter iters/s
============================================================================
crc32_512 55.73ns 17.94M
crc32_1024 85.15ns 11.74M
crc32_2048 116.29ns 8.60M
crc32_4096 191.03ns 5.23M
crc32_8192 341.44ns 2.93M
crc32_16384 627.76ns 1.59M
crc32_32768 1.21us 827.16K
============================================================================
Comparison:

============================================================================
[...]folly/hash/test/ChecksumBenchmark.cpp relative time/iter iters/s
============================================================================
crc32_512 1.80us 554.82K
crc32_1024 3.58us 279.35K
crc32_2048 7.14us 140.13K
crc32_4096 14.25us 70.18K
crc32_8192 28.47us 35.12K
crc32_16384 56.93us 17.57K
crc32_32768 113.83us 8.79K
```