Consider doing only a "check" build of libstd

[RalfJung]

Somewhere (I forgot) I got the recommendation to try and make Miri only do a "check" build of libstd, instead of doing a full "build". That could help circumventing rust-lang/rust#56443, which in turn would hopefully enable Miri to cross-interpret programs for any target.

I am unsure whether we should do this by extending xargo with support for "check" builds, or whether we should just copy the relevant parts of xargo and thus kill that dependency. I am not sure how much would have to be copied.

Cc @oli-obk

[oli-obk]

No clue what the right way would be here. I'm not even sure what "all the things that xargo does" are. Maybe we can just call cargo check on a checkout of libstd?

[RalfJung]

I'm not even sure what "all the things that xargo does" are

Same. I think it boils down to preparing a Cargo.toml in a tmpdir and calling cargo with the right flags and env vars.

Maybe we can just call cargo check on a checkout of libstd?

It should work with what is in the rust-src component, which is not a complete workspace.

[bjorn3]

And it then copies the right files into the correct sysroot layout and then builds libtest in a way I dont yet understand.

[RalfJung]

Ah good point, we need libtest as well.

[RalfJung]

@Aaron1011 is working on the basics for this in xargo, with the goal of resolving rust-lang/rust#66247.

[RalfJung]

Closing in favor of #1057.