DXBC support

[disks86]

If possible it would be helpful to have DXBC to SPIR-V conversion support. To be perfectly honest it would save me the trouble of writing it for my project VK9.
https://github.com/disks86/VK9

[gongminmin]

I do have a project about trans-compile DXBC to GLSL https://github.com/gongminmin/KlayGE/tree/develop/DXBC2GLSL. I don't think it would be hard to retarget it to SPIR-V. But I don't have enough time to do it for now. Could be a goal of Dilithium in the future.