Replace spaghetti with a simple errors enum

compiler/rustc_driver/src/session_diagnostics.rs

@@ -1,4 +1,3 @@
-use rustc_codegen_ssa::session_diagnostic::DeserializeRlinkError;
 use rustc_macros::SessionDiagnostic;
 
 #[derive(SessionDiagnostic)]
@@ -8,9 +7,25 @@ pub(crate) struct RlinkUnableToRead {
 }
 
 #[derive(SessionDiagnostic)]
-#[diag(driver::rlink_unable_to_deserialize)]
-pub(crate) struct RlinkUnableToDeserialize {
-    pub err: DeserializeRlinkError,
+#[diag(driver::rlink_wrong_file_type)]
+pub(crate) struct RLinkWrongFileType;
+
+#[derive(SessionDiagnostic)]
+#[diag(driver::rlink_empty_version_number)]
+pub(crate) struct RLinkEmptyVersionNumber;
+
+#[derive(SessionDiagnostic)]
+#[diag(driver::rlink_encoding_version_mismatch)]
+pub(crate) struct RLinkEncodingVersionMismatch {
+    pub version_array: String,
+    pub rlink_version: String,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(driver::rlink_rustc_version_mismatch)]
+pub(crate) struct RLinkRustcVersionMismatch {
+    pub rustc_version: String,
+    pub current_version: String,
 }
 
 #[derive(SessionDiagnostic)]