Add fixes for Caching and rustc-dep-of-std feature

[josephlr]

We now cache the Cargo index (among other things) in our CI. This prevents some spurious test failures on Windows.

Also, Properly forward rustc-dep-of-std feature

[newpavlov]

IIRC on aarch64 Hermit simply always returns an error, did this situation change? In other words, any use of HashMap with such code would result in a panic, so the existing exception in the std integration PR looks like a better choice for now. Personally, I would prefer for hermit-os/kernel#143 to be solved first and for getrandom to use the new API.

The CI changes are probably better done in a separate PR.

[newpavlov]

I like all changes, except the Hermit addition. :) How about removing the Hermit part for now, renaming this PR, and opening a tracking issue for the Hermit part?

@stlankes
Any ETA on adding a Linux-like syscall to Hermit as described in the linked issue?

[josephlr]

I like all changes, except the Hermit addition. :) How about removing the Hermit part for now, renaming this PR, and opening a tracking issue for the Hermit part?

Done. This PR now just contains the caching and rustc-dep-of-std fixes.

[josephlr]

#199 is now open to track all hermit <-> getrandom issues. Further discussion should continue there.

[stlankes]

A small comment to the ARM port, it comes, but the current version isn't stable. It takes some time.