build: keep the actual clang-<major> when trimming LLVM (clang-23 was deleted)

[liminfei-amd]

Fixes #16.

What

The "Trim LLVM toolchain" step kept only clang and a hardcoded clang-22, but the bundled LLVM is major 23. The clang driver re-execs clang-23, which the keep-list didn't match — so clang-23 was deleted. The shipped bundle has the clang driver but no clang-23, and Triton's JIT fails with could not exec .../clang-23.

Change

Derive the LLVM major from the resource dir lib/clang/<major> (fallback clang -dumpversion) and keep clang-${major} + its cuda_wrappers path, instead of hardcoding 22. Stays correct across LLVM bumps.

-        # Keep only clang, clang-22, remove everything else from bin/
-        find "$LLVM/bin" -type f ! -name "clang" ! -name "clang-22" -delete
+        CLANG_MAJOR="$(ls "$LLVM/lib/clang" | grep -E '^[0-9]+$' | sort -n | tail -1)"
+        [ -z "$CLANG_MAJOR" ] && CLANG_MAJOR="$("$LLVM/bin/clang" -dumpversion | cut -d. -f1)"
+        find "$LLVM/bin" -type f ! -name "clang" ! -name "clang-${CLANG_MAJOR}" -delete
...
-        rm -rf "$LLVM/lib/clang/22/include/cuda_wrappers"
+        rm -rf "$LLVM/lib/clang/${CLANG_MAJOR}/include/cuda_wrappers"

Evidence

On the released vllm0.22.1-rocm7.13.0-gfx1151 bundle: bin/clang-23 is absent (only the 26 KB clang driver), lib/clang/23/ + libclang-cpp.so.23 are present, and clang --version errors with could not exec .../clang-23. Triton JIT then fails; supplying a system clang lets it compile.

Verification (honest)

I did not re-run the full build CI myself. This repo's pull_request build + the gfx1151 qualification (tier2 inference uses Triton) are the right place to confirm the rebuilt bundle keeps clang-23 and that Triton-based inference passes. Opening as draft for that reason and for maintainer review of the approach.

AI usage disclosure: this change was prepared with AI assistance; a human reviewed and verified it and can explain every line. Verified: missing-binary + JIT failure reproduced on the released bundle.