x test src/tools/lint-docs fails when download-rustc is enabled

[jyn514]

I tried this code: ./configure --set download-rustc && x test src/tools/lint-docs

I expected to see this happen: All tests pass.

Instead, this happened:

Building tool lint-docs (stage0)
    Finished release [optimized] target(s) in 0.10s
error: failed to test example in lint docs for `forbidden_lint_groups` in /home/jyn/src/rust/compiler/rustc_lint_defs/src/builtin.rs:11: did not find lint `forbidden_lint_groups` in output of example, got:
/home/jyn/src/rust/build/x86_64-unknown-linux-gnu/stage2/bin/rustc: symbol lookup error: /home/jyn/src/rust/build/x86_64-unknown-linux-gnu/stage2/lib/librustc_driver-51fc469e8c788ca6.so: undefined symbol: LLVMInitializeLoongArchTargetInfo, version LLVM_16

This looks like the same issue as #110226; not sure why #110263 didn't fix it.

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HEAD is branched from ce1073b.

[jyn514]

Note that x test linkchecker depends on lint-docs / src/doc/rustc; when you fix this issue you should also double check that x test linkchecker is fixed.