Optimize LLVM workflow host tools

[awakecoding]

Summary

• reduce the native host-tools build to only the tools required by the target LLVM build
• configure host tools with LLVM_TARGETS_TO_BUILD=Native and disable unnecessary host-side extras
• detect and use lld-link for Windows LLVM configures when available

Validation

• parsed .github/workflows/llvm-prebuilt.yml as YAML
• ran git diff --check
• triggered llvm-prebuilt.yml on this branch: https://github.com/awakecoding/llvm-prebuilt/actions/runs/26717525213
• CI signal before opening: several macOS/Ubuntu matrix legs completed successfully, all remaining jobs were still running with no failures observed