[libclc] [libclc] Add an option to build SPIR-V targets with the LLVM backend (PR #151347)

[Konrad Kleine via cfe-commits]

kwk wrote:

Okay, I ran a test again with revision from 25th November 2025 (2f8e71287542a597be246d34699c93345d096f22).

The file that runs into high memory consumption is this one:

```console
bash-5.3# ls -lha /builddir/build/BUILD/llvm-22.0.0_pre20251125.g2f8e71287542a5-build/llvm-project-2f8e71287542a597be246d34699c93345d096f22/llvm/redhat-linux-build/./bin/../lib/clang/22/lib/libclc/gfx1251-amdgcn--.bc
lrwxrwxrwx. 1 mockbuild mock 18 Nov 25 10:52 /builddir/build/BUILD/llvm-22.0.0_pre20251125.g2f8e71287542a5-build/llvm-project-2f8e71287542a597be246d34699c93345d096f22/llvm/redhat-linux-build/./bin/../lib/clang/22/lib/libclc/gfx1251-amdgcn--.bc -> tahiti-amdgcn--.bc
```

The actual link target is this:

```console
bash-5.3# ls -lha /builddir/build/BUILD/llvm-22.0.0_pre20251125.g2f8e71287542a5-build/llvm-project-2f8e71287542a597be246d34699c93345d096f22/llvm/redhat-linux-build/./bin/../lib/clang/22/lib/libclc/tahiti-amdgcn--.bc
-rw-r--r--. 1 mockbuild mock 6.2M Nov 25 10:52 /builddir/build/BUILD/llvm-22.0.0_pre20251125.g2f8e71287542a5-build/llvm-project-2f8e71287542a597be246d34699c93345d096f22/llvm/redhat-linux-build/./bin/../lib/clang/22/lib/libclc/tahiti-amdgcn--.bc
```

At the beginning of the compilation:

<img width="1864" height="892" alt="image" src="https://github.com/user-attachments/assets/1ce134a0-47ed-40ee-8af4-5a2883087f56" />

During high memory consumption:

<img width="1864" height="892" alt="image" src="https://github.com/user-attachments/assets/4f1359df-1c0b-41c4-b72a-6d631e8314cf" />

Failing:

<img width="1869" height="879" alt="image" src="https://github.com/user-attachments/assets/b3723583-1e3b-4b6c-8750-fa8ae5e9fef8" />


https://github.com/llvm/llvm-project/pull/151347