Avoid no-op unlink+link dances in incr comp

compiler/rustc_codegen_ssa/src/base.rs

@@ -656,6 +656,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
                 bytecode: None,
                 assembly: None,
                 llvm_ir: None,
+                links_from_incr_cache: Vec::new(),
             }
         })
     });