Need to take endianness into account when doing vector to scalar casts such as
%bc = bitcast <8 x i1> %v to i8
Companion review for https://reviews.llvm.org/D94867
Upload in response to https://lists.llvm.org/pipermail/llvm-dev/2021-January/147862.html
Attempting to document the actual memory layout rules for vectors in https://reviews.llvm.org/D94964
It's a shame we can't just use extract elements - that would simplify this a lot!