make Libtask compatible with Julia 1.6

[KDr2]

Not ready to merge until JuliaPackaging/Yggdrasil#2176 is merged.

[devmotion]

Looks good to me but I guess we have to wait until Julia 1.6 is released (or at least one can build binaries for Julia 1.6 on Yggdrasil).

On the other hand, it does not break anything on Julia < 1.6 and only improves the code, so we could also merge it now. It is just not guaranteed that these fixes are sufficient for Julia 1.6.

[KDr2]

On the other hand, it does not break anything on Julia < 1.6 and only improves the code, so we could also merge it now.

Agree.

It is just not guaranteed that these fixes are sufficient for Julia 1.6.

I ran the unit tests locally (on linux) with the updated C source, all of them passed.

So it seems that this PR can be merged now.

[devmotion]

Good I trust you 🙂 And if we notice any problems in the future, we can always make a bugfix release.

I guess it would be useful to make a release right away if people want to use it with Julia master (even though I don't think it's very likely since they would have to build everything manually)?

[yebai]

Great work, thanks @KDr2!