The original patch had a reasonably significant bug. You could not use
`.insn` to assemble encodings that had any bits set above the low 32
bits. This is due to the fact that `getMachineOpValue` was truncating
the immediate value, and I did not commit enough tests of useful cases.
This changes the result of `getMachineOpValue` to be able to return the
48-bit and 64-bit immediates needed for the wider `.insn` directives.
I took the opportunity to move some of the test cases around in the file
to make looking at the output of `llvm-objdump` a little clearer.
b5ea5be2a7