Rollup merge of #86113 - the8472:doctest-lld, r=Mark-Simulacrum

build doctests with lld if use-lld = true

results when running `./x.py test library/core --doc --stage 0`:

```
# OLD
test result: FAILED. 2844 passed; 6 failed; 28 ignored; 0 measured; 0 filtered out; finished in 21.13s

# NEW
test result: FAILED. 2844 passed; 6 failed; 28 ignored; 0 measured; 0 filtered out; finished in 11.92s
```