Fix clippy::needless_borrow in the compiler

`x clippy compiler -Aclippy::all -Wclippy::needless_borrow --fix`.

Then I had to remove a few unnecessary parens and muts that were exposed
now.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -853,7 +853,7 @@ pub fn build_compile_unit_di_node<'ll, 'tcx>(
 
     use rustc_session::RemapFileNameExt;
     let name_in_debuginfo = name_in_debuginfo.to_string_lossy();
-    let work_dir = tcx.sess.opts.working_dir.for_codegen(&tcx.sess).to_string_lossy();
+    let work_dir = tcx.sess.opts.working_dir.for_codegen(tcx.sess).to_string_lossy();
     let flags = "\0";
     let output_filenames = tcx.output_filenames(());
     let split_name = if tcx.sess.target_can_use_split_dwarf() {

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/cpp_like.rs

@@ -715,7 +715,7 @@ fn build_union_fields_for_direct_tag_coroutine<'ll, 'tcx>(
                 coroutine_type_and_layout,
                 coroutine_type_di_node,
                 coroutine_layout,
-                &common_upvar_names,
+                common_upvar_names,
             );
 
             let span = coroutine_layout.variant_source_info[variant_index].span;

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/native.rs

@@ -197,7 +197,7 @@ pub(super) fn build_coroutine_di_node<'ll, 'tcx>(
                                 coroutine_type_and_layout,
                                 coroutine_type_di_node,
                                 coroutine_layout,
-                                &common_upvar_names,
+                                common_upvar_names,
                             ),
                         source_info,
                     }