chore: Build for riscv64gc

[pavelzw]

Description

with riscv support on conda-forge gaining traction (conda-forge/conda-forge.github.io#1744), we should also support it in rattler-based tooling.

Fixes #{issue}

How Has This Been Tested?

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Checklist:

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[h-vetinari]

how did you choose the architecture abbreviation here? Why riscv64gc rather than (say) riscv64?

[h-vetinari]

Ah, I see from conda/rattler#1949 that you're following rust terminology? Can you add a comment about any/all this in conda-forge/conda-forge.github.io#1744? I'd like to avoid having different names for the same architecture in different places. I'm willing to be convinced that we should follow rust's naming if necessary, but by default I was expecting to use riscv64.

[h-vetinari]

C.f. also conda/conda-build#5884; I'd expect to be able to do

  - if: riscv64
    then:
      - something

in v1 recipes