Summary:
disable UBSAN for functions with intentional left shift on -ve number / overflow
These functions are
rocksdb:: Hash
FixedLengthColBufEncoder::Append
FaultInjectionTest:: Key
Closes https://github.com/facebook/rocksdb/pull/1577
Differential Revision: D4240801
Pulled By: IslamAbdelRahman
fbshipit-source-id: 3e1caf6