Move metadata object generation for dylibs to the linker code

This deduplicates some code between codegen backends and may in the
future allow adding extra metadata that is only known at link time.

Author: bjorn3

src/lib.rs

@@ -48,7 +48,6 @@ extern crate rustc_index;
 #[cfg(feature = "master")]
 extern crate rustc_interface;
 extern crate rustc_macros;
-extern crate rustc_metadata;
 extern crate rustc_middle;
 extern crate rustc_session;
 extern crate rustc_span;
@@ -106,7 +105,6 @@ use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen, TargetCon
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::IntoDynSyncSend;
 use rustc_errors::DiagCtxtHandle;
-use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::util::Providers;
@@ -230,9 +228,9 @@ impl CodegenBackend for GccCodegenBackend {
         providers.global_backend_features = |tcx, ()| gcc_util::global_gcc_features(tcx.sess, true)
     }
 
-    fn codegen_crate(&self, tcx: TyCtxt<'_>, metadata: Option<&EncodedMetadata>) -> Box<dyn Any> {
+    fn codegen_crate(&self, tcx: TyCtxt<'_>) -> Box<dyn Any> {
         let target_cpu = target_cpu(tcx.sess);
-        let res = codegen_crate(self.clone(), tcx, target_cpu.to_string(), metadata);
+        let res = codegen_crate(self.clone(), tcx, target_cpu.to_string());
 
         Box::new(res)
     }