Upgrade taichi to support LLVM20

[duburcqa]

For reference: Genesis-Embodied-AI/genesis-world#1274

[johnnynunez]

im working on it. Also to add cuda arm @duburcqa

[duburcqa]

Great! Thank you!

[johnnynunez]

Great! Thank you!

I will do small changes (a lot of PRs) @hughperkins

[hughperkins]

Note: I have a gentle preference to go via llvm 18 first, because it seems fairly widely available, and because llvm 15 is so old. But it's just a gentle preference: as long as things build and run correctly across all platforms - Windows, Mac, Ubuntu - I don't have any major objection to hopping directly to llvm 20.

[johnnynunez]

Note: I have a gentle preference to go via llvm 18 first, because it seems fairly widely available, and because llvm 15 is so old. But it's just a gentle preference: as long as things build and run correctly across all platforms - Windows, Mac, Ubuntu - I don't have any major objection to hopping directly to llvm 20.

Agree but not at all. Cuda 13 is compatible with llvm 20

[hughperkins]

Could we split this issue into two please? One for llvm20 upgrade (and justification); and one for vulkan upgrade (and justificaiton).

Note that currently we are using 1.4.304.1 on linux, but 1.3.296.0 Windows. Looks easy to upgrade, but lets split into a separate issue please.

Actually I'll go ahead and create a separate issue for vulkan upgrade; and modify the title of this issue.

[hughperkins]

(split out vullkan 1.4.313 to separate issue)

[hughperkins]

closed in #275