Ensure -V --verbose processes both codegen_backend and codegen-backend

Author: danielframpton

compiler/rustc_driver_impl/src/lib.rs

@@ -1112,7 +1112,10 @@ fn get_backend_from_raw_matches(
     matches: &Matches,
 ) -> Box<dyn CodegenBackend> {
     let debug_flags = matches.opt_strs("Z");
-    let backend_name = debug_flags.iter().find_map(|x| x.strip_prefix("codegen-backend="));
+    let backend_name = debug_flags.iter().find_map(|x| {
+        x.strip_prefix("codegen")
+            .and_then(|x| x.strip_prefix("-backend=").or_else(|| x.strip_prefix("_backend=")))
+    });
     let target = parse_target_triple(early_dcx, matches);
     let sysroot = filesearch::materialize_sysroot(matches.opt_str("sysroot").map(PathBuf::from));
     let target = config::build_target_config(early_dcx, &target, &sysroot);