swift234

Replace the use of llvm::hash in getGenericMetadata with a fast hash implementation.

Before the change we were spending ~35% of the time of getGenericMetadata in hashing the inputs. I measured the following speedups:

SwiftStructuresQueue  1.11x
Havlak                1.11x
CaptureProp           1.11x
SwiftStructuresStack  1.12x
Life                  1.15x
NestedLoop            1.16x
RangeAssignment       1.24x

Swift SVN r23708