session: diagnostic migration lint on more fns

Apply the diagnostic migration lint to more functions on `Session`.

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -305,8 +305,12 @@ impl TargetMachineFactoryConfig {
 }
 
 pub type TargetMachineFactoryFn<B> = Arc<
-    dyn Fn(TargetMachineFactoryConfig) -> Result<<B as WriteBackendMethods>::TargetMachine, String>
-        + Send
+    dyn Fn(
+            TargetMachineFactoryConfig,
+        ) -> Result<
+            <B as WriteBackendMethods>::TargetMachine,
+            <B as WriteBackendMethods>::TargetMachineError,
+        > + Send
         + Sync,
 >;
 

compiler/rustc_codegen_ssa/src/traits/write.rs

@@ -8,6 +8,7 @@ use rustc_middle::dep_graph::WorkProduct;
 pub trait WriteBackendMethods: 'static + Sized + Clone {
     type Module: Send + Sync;
     type TargetMachine;
+    type TargetMachineError;
     type ModuleBuffer: ModuleBufferMethods;
     type ThinData: Send + Sync;
     type ThinBuffer: ThinBufferMethods;