Add an attempt to build upstream libxml2-nokogiri with patches

[loz]

Note this is response to a twitter thread with @tenderlove around trying to build some disti packages to speed up install of the gem, if the disti build could already have a custom build.

1. This doesn't sort the consumption of a disti version in the gem build (yet)
2. This hasn't published, and only currently targets alpine, however there is a docker file which could be used to CI test that a package builds, and that nokogiri can install (when integrated)
3. Is hardcoded in the APKBUILD file which could probably be autogenerated from other artefacts in the repo
4. Needs to be integrated into a CI for publish, and in particular publish a PR to alpine for the build (I think) into a blessed alpine REPO.

What problem is this PR intended to solve?

This is a build/APK setup to build a custom alpine package for libxml

Have you included adequate test coverage?

No nokogiri changes, just added some APK stuff

Does this change affect the C or the Java implementations?

No

If not, that may be OK, just please note it here.

[codeclimate]

Code Climate has analyzed commit 54bb8e0 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (80% is the threshold).

This pull request will bring the total coverage in the repository to 93.5%.

View more on Code Climate.

[flavorjones]

@loz Thanks for submitting this. I have to admit I'm not totally sure what the goal of this PR is, can you maybe start from the beginning and assume I'm not familiar with the aforementioned twitter thread?

This sounds a little like you're trying to precompile libxml? And if that's the case we've already got a plan at #1571 which is simply awaiting additional tests that install the gem and exercise the test suite (see also #1845).

[loz]

That is indeed the thread, around pre-installing/using pre-installed native binaries which are safe, and free from XSF etc.. Looks like this is covered, so closing out.