Addresses #3809: when we are asked to create a Cranelift backend with
shared flags that indicate support for SIMD, we should check that the
ISA level needed for our SIMD lowerings is present.
Implemented the following Opcodes for the Cranelift interpreter:
- `VhighBits` to reduce a vector to a scalar integer formed by
concatenating the MSB of each lane.
- `Vselect` to select lanes from two vectors controlled by a boolean
vector.
Copyright (c) 2021, Arm Limited
