Switch Requires.jl to weakdep

[oscardssmith]

julia> @time using Quadmath
  0.009195 seconds (8.15 k allocations: 549.961 KiB, 34.84% compilation time) # before
  0.006442 seconds (4.01 k allocations: 305.828 KiB) #after

[DilumAluthge]

Looks like Windows CI is failing?

[DilumAluthge]

Is this change (dropping support for Julia 1.6 through 1.9) intentional?

[oscardssmith]

yes (but I can make this work on older versions if desired)

[DilumAluthge]

I think we can just do #88 (comment), and thus not need to drop support for Julia 1.6 through 1.9 (but we still get the benefit of getting rid of Requires.jl).

[DilumAluthge]

Actually, I don't even think we need to drop support for Julia 1.6 through 1.9. Instead, we can do the following:

1. On Julia versions 1.6 through 1.9, make SpecialFunctions a regular direct dep.
2. On Julia 1.10+, make SpecialFunctions a weakdep.

Basically, following the instructions in the "Transition from normal dependency to extension" section here: https://pkgdocs.julialang.org/v1/creating-packages/#Transition-from-normal-dependency-to-extension

[DilumAluthge]

And then, since we aren't dropping support for any old Julia versions, we can just do the patch version bump of 0.5.13 ---> 0.5.14.

[DilumAluthge]

Either way, we do need to fix Windows CI on this PR.

[DilumAluthge]

@oscardssmith Do you have an idea as to why Windows CI is failing on this PR?

I just checked, and all CI is green on master (see e.g. #90), so the CI failure does seem related to the contents of this PR.

[oscardssmith]

I have no idea. Pkg extensions really shouldn't be OS specific, so while I agree that this PR causes the failures, I haven't the faintest idea why.

[oscardssmith]

Cody helped me figure out the problem. The issue was that this package made it's own fake @ccall that we weren't importing. I've renamed it to make this slightly less horrible (but I would like to delete this macro entirely)

[oscardssmith]

So is this good to merge? (or do we want to do the version with Requires to allow backward compat to 1.6?)

[DilumAluthge]

How about we do #88 (comment)? (Which doesn't use Requires.jl).

[oscardssmith]

changes made

[DilumAluthge]

CI failures will be fixed by #91.