Gate explicit macOS libxml2 linking behind vendored-extra feature

[HadrienG2]

Per @nazar-pc comment in #98 .

[semanticdiff-com[bot]]

Review changes with SemanticDiff.

Analyzed 1 of 2 files.

Overall, the semantic diff is 48% smaller than the GitHub diff.

	Filename	Status
:grey_question:	hwlocality-sys/Cargo.toml	Unsupported file format
:heavy_check_mark:	hwlocality-sys/build.rs	47.93% smaller

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (01ae3b6) 65.28% compared to head (ec0f695) 65.28%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #99 +/- ## ======================================= Coverage 65.28% 65.28% ======================================= Files 43 43 Lines 4632 4632 ======================================= Hits 3024 3024 Misses 1608 1608 ``` | [Flag](https://app.codecov.io/gh/HadrienG2/hwlocality/pull/99/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Hadrien+G.) | Coverage Δ | | |---|---|---| | [ubuntu-latest](https://app.codecov.io/gh/HadrienG2/hwlocality/pull/99/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Hadrien+G.) | `66.53% <ø> (ø)` | | | [windows-latest](https://app.codecov.io/gh/HadrienG2/hwlocality/pull/99/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Hadrien+G.) | `63.94% <ø> (+0.04%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Hadrien+G.#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.