This is somewhat awkward to support, but the best effort we can do here
is to analyze various Load/Store opcodes and deduce the ideal overall
alignment based on this. This is not a 100% perfect solution, but should
be correct for any reasonable use case.
Also fix various nitpicks with BDA support while I'm at it.
Buffer objects can contain arbitrary pointers to blocks.
We can also implement ConvertPtrToU and ConvertUToPtr.
The latter can cast a uint64_t to any type as it pleases,
so we will need to generate fake buffer reference blocks to be able to
cast the type.