Make `.pkg/select_artifacts.jl` parse riscv64

[giordano]

This line

BinaryBuilder.jl/src/AutoBuild.jl

Line 1431 in 4538e89

platform = augment_platform!(HostPlatform(parse(Platform, target_triplet)))

freaks out on Julia < 1.12 (and in particular v1.7 used in Yggdrasil) when trying to parse a triplet like riscv64-linux-gnu: JuliaPackaging/Yggdrasil#10503 (comment). We need to make parse(::Type{Platform}, ::String) digest riscv64 as an architecture for Julia < 1.12 only. Basically a smaller version of https://github.com/JuliaPackaging/BinaryBuilderBase.jl/blob/bc1c293e367714537136d22ece9d81a82731b009/src/riscv64.jl, only whatever is needed for parsing, probably only the parse method at https://github.com/JuliaPackaging/BinaryBuilderBase.jl/blob/bc1c293e367714537136d22ece9d81a82731b009/src/riscv64.jl#L92, without all the rest, we don't need anything of the rest.

@eschnett I think you were motivated to look into this? I don't have much time to work on this myself at the moment, it should be fairly simple, only doing the minimal changes to make parsing work correctly.

[eschnett]

I'm looking at this now.

[eschnett]

I'm still getting

ERROR: LoadError: ArgumentError: Platform `riscv64-linux-gnu-libgfortran5-cxx11-mpi+mpich` is not an officially supported platform

when building HDF5. Investigating... I thought this worked?

[eschnett]

Am I just confused? Do we need to rebuild MPICH etc. with this new version of BinaryBuilder?

[giordano]

We need to:

1. update BinaryBuilder in Yggdrasil
2. rebuild relevant packages

Nothing else to do here.