rocksdb: sync with upstream

to pick up
- bug fixes since 5.8.0
- crc32c_3way introduced in 5.9.0 for better performance on platforms
with PCLMULQDQ support.
- the fixes for silencing the fallthrough warnings when compiling with
GCC-7

for detailed changelog since 5.8.0, see
https://github.com/facebook/rocksdb/blob/master/HISTORY.md

Signed-off-by: Kefu Chai <kchai@redhat.com>