[clang] [llvm] [SPIR-V] Add SPIR-V structurizer (PR #107408)

[Nathan Gauër via cfe-commits]

Keenuts wrote:

Thanks for looking into this.
I don't know what's causing the ""Virtual register defs don't dominate all uses", as some cases are located in the middle of a block and doesn't seem to be related to BB sorting (even though this is probably the cause)

```
127 bb.10.do.end8:
[...]
133   %96:iid(s32) = nsw G_ADD %97:iid, %98:iid
134   %97:iid(s32) = GET_ID %45:iid(s32)
[...]
139   G_BR %bb.11
```

Need to investigate this.
Also will investigate the hang you observe.

https://github.com/llvm/llvm-project/pull/107408