vkd3d: DXIL2SPIRV progress update

[Hans-Kristian Arntzen]

Hi. I've gotten a lot further on DXIL, and I've worked on translating 
PHI better and some actual codegen. It's getting quite workable now and 
a fair amount of opcodes are translated, but it's a long road ahead. 
Reasonably interesting code can be converted now, e.g.:

https://gist.github.com/HansKristian-Work/df272ad97dc879514fdd494798b5296d.

Once things come together I'll try to get this working in vkd3d.

Cheers,
Hans-Kristian