Change LoadAndStorePromoter to take ArrayRef instead of SmallVectorImpl&.

The array passed to LoadAndStorePromoter's constructor was a constant reference to a SmallVectorImpl, which is just the same as passing an ArrayRef.

Also, the data in the array can be 'const Instruction*' instead of 'Instruction*'.  Its not possible to convert a SmallVectorImpl<T*> to SmallVectorImpl<const T*>, but ArrayRef does provide such a method.

Currently this added calls to makeArrayRef which should be a nop, but i'm going to kick off a discussion about improving ArrayRef to not need these.

llvm-svn: 237226