Add Android support

[mhsmith]

This will be used by cibuildwheel to replace its limited built-in support for adding external libraries to an Android wheel.

This involves cross-compilation, but it doesn't have much of an overlap with #512. It adds the --ldpaths option, which allows auditwheel to search an arbitrary sysroot, rather than the build machine's own libraries.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.62%. Comparing base (d5801df) to head (e0bf5ba).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #643      +/-   ##
==========================================
+ Coverage   95.24%   95.62%   +0.38%     
==========================================
  Files          22       23       +1     
  Lines        1829     1897      +68     
  Branches      343      357      +14     
==========================================
+ Hits         1742     1814      +72     
+ Misses         48       46       -2     
+ Partials       39       37       -2     

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[mhsmith]

I don't know why codecov is generating so much noise in the timeline; I'm not doing anything except pushing commits. It wasn't doing this last week.

[mayeut]

I don't know why codecov is generating so much noise in the timeline; I'm not doing anything except pushing commits. It wasn't doing this last week.

I moved the token in an environment as recommended by zizmor but this is now failing on PR. I need to check how to silence this. Sorry for the noise.

[mhsmith]

This PR is ready for review.

[mayeut]

thanks @mhsmith

Given the size and scope of the PR it might take a bit of time to review properly.

One thing that comes to mind not digging deeply into this is:
cibuildwheel allows cross-building Android wheels from Linux or macOS if I'm not mistaken, so auditwheel probably needs to work on macOS for that use-case and thus be tested on macOS. I'm not sure how it would affect what's already done here but probably worth checking before a thorough review.

[mhsmith]

Yes, in fact my desktop machine uses macOS, so I used it for almost all of my testing. I guess this means we should add a CI job for that platform as well, but I'll wait for your review before I deal with that.