Rollup merge of #157050 - bjorn3:lto_refactors19, r=lqd

Couple of changes to help with moving LTO to the link phase

Part of rust-lang/compiler-team#908

Author: JonathanBrouwer

src/lib.rs

@@ -339,9 +339,7 @@ fn new_context<'gcc, 'tcx>(tcx: TyCtxt<'tcx>) -> Context<'gcc> {
 }
 
 impl ExtraBackendMethods for GccCodegenBackend {
-    fn supports_parallel(&self) -> bool {
-        false
-    }
+    type Module = GccContext;
 
     fn codegen_allocator(
         &self,
@@ -424,6 +422,10 @@ impl WriteBackendMethods for GccCodegenBackend {
     type ModuleBuffer = ModuleBuffer;
     type ThinData = ();
 
+    fn supports_parallel(&self) -> bool {
+        false
+    }
+
     fn target_machine_factory(
         &self,
         _sess: &Session,