evaluateBranch currently takes a single instruction. This works for most
targets, but is insufficient for e.g. auipc+jalr pairs on RISC-V. This
commit adds a new optional argument for the previous instruction,
allowing these targets to implement evaluateBranch for such instruction
This patch simply adds the argument, and modifies llvm-objdump to pass
This isn't a pretty solution, so if you have alternate proposals I'd be keen to discuss.