Add llvm-xtensa and ldc-xtensa images

[Reavershark]

Builds llvm from https://github.com/espressif/llvm-project, and ldc with that llvm build.
These are seperate images from ldc and llvm because I can't find any good way to add this along the existing ldc and llvm version tags.
Currently building with ./ddct ldc-xtensa 1.39 one last time from scratch. Will confirm here if it works.

Upstream llvm has very limited Xtensa support which is easy to enable as experimental target, and might be done even by upstream ldc (ldc-developers/ldc#4725), as is already the case with SPIR-V.
To actually compile for xtensa esp32 chips, you need the not-yet-upstreamed espressif fork of llvm.

[0xEAB]

To actually compile for xtensa esp32 chips, you need the not-yet-upstreamed espressif fork of llvm.

This (as in the fork, not your comment) doesn’t feel right. Is there an official statement on the reasoning why they haven’t properly upstreamed their patches yet?

[Reavershark]

See espressif/llvm-project#4 (comment), espressif/llvm-project#4 (comment).
It seems that their fork was developed separately but works, but the llvm team won't work with one huge pr.
The last couple of years they've been slowly preparing smaller patches and getting them merged into llvm:main.

[Reavershark]

This pr works now (had some issues after rebasing).