fix: get_cpu_value for bazel 8.0.0rc4

[kczulko]

Attempt to fix #612

[avdv]

Hi @kczulko, I don't know if you've seen this, but the get_cpu_value function in rules_cc is private, and we thought vendoring a copy of it would be a better solution.

[kczulko]

Hi Claudio,

I thought I could reference this function. However, legacy workspace dependency hell is a bit more complex to solve in comparison to "just changing" the place from which we take get_cpu_value function. I'll follow your advice. Thx!

[malt3]

Thank you very much!

[kczulko]

@malt3
Maybe it's worth to drop it: bazelbuild/rules_cc#283

[malt3]

Thanks for the pointer. As you pointed out, upgrading rules_cc is not a trivial change in rules_nixpkgs at this point, so your PR is still good for the moment.