rust-hypervisor-firmware: fix build (#257345)

Co-authored-by: Yureka <[e-mail]>

pkgs/applications/virtualization/rust-hypervisor-firmware/default.nix

···
 { lib
 , fetchFromGitHub
-, makeRustPlatform
 , hostPlatform
 , targetPlatform
+, cargo
+, rustc
 , lld
 }:
 
···
     };
   };
 
-  inherit (cross) rustPlatform;
+  # inherit (cross) rustPlatform;
+  # ^ breaks because we are doing a no_std embedded build with a custom sysroot,
+  # but the fast_cross rustc wrapper already passes a sysroot argument
+  rustPlatform = cross.makeRustPlatform {
+    inherit rustc cargo;
+  };
 
 in