Test using this for bfcc

[skx]

The assembly output by bfcc should now be able to compiled by this assembler.

Of course we'll need to tweak the output to use registers we know about - e.g. rbp rather than r8, but I think I've now handled all the obvious instructions so that'll be the big test.

The most likely problem will be the byte-offset limitation of our jmp, jnz, jz instructions. We'll see if it will work.