buildRustCrate: Add support for standard library deps
We are replicating one mechanism behind `-Z build-std`.
There isn't yet crate2nix support for this, but one can (and I do) add
the missing stdlib deps (for this feature to pick up) with overrides.
(cherry picked from commit cc29693a0979c3b81da6942c214841ef11de95b5)
(cherry picked from commit 5aef865cefc2a906296b9a256bf597f70e4ee243)
