There's a closed pull request on the void-packages repository

flightgear: update to 2020.3.13
https://github.com/void-linux/void-packages/pull/37106

Description:
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#### Testing the changes
- I tested the changes in this PR: **YES**

I removed the qt option because: 1) according to the git history, building without qt allowed cross builds, but it's not necessary now; 2) the package is big anyway; 3) nobody complained that's it's currently broken, so I think nobody uses it.

The time64 patch for musl 1.2 was dropped by Alpine, so I guess Void won't need it either.

I figured out how to build the test suites for both packages, but they segfault (on previous versions too), though the installed program works fine. I'll probably open an issue upstream later.
Does it make sense to enable the tests and add `make_check=no`?