disable cross-crate specs for unsafe core proof

Author: Aurel300

prusti/src/callbacks.rs

@@ -156,7 +156,12 @@ impl prusti_rustc_interface::driver::Callbacks for PrustiCompilerCalls {
                     println!("{value}");
                 }
             }
-            CrossCrateSpecs::import_export_cross_crate(&mut env, &mut def_spec);
+
+            // FIXME: `prusti-std` has specs which unsafe core proof does not support
+            if !config::unsafe_core_proof() {
+                CrossCrateSpecs::import_export_cross_crate(&mut env, &mut def_spec);
+            }
+
             if !config::no_verify() {
                 verify(env, def_spec);
             }