Remove redundant path join

Author: cbeuw

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1055,14 +1055,11 @@ pub fn compile_unit_metadata(
     let work_dir = tcx.sess.opts.working_dir.to_string_lossy(FileNameDisplayPreference::Remapped);
     let flags = "\0";
     let output_filenames = tcx.output_filenames(());
-    let out_dir = &output_filenames.out_directory;
     let split_name = if tcx.sess.target_can_use_split_dwarf() {
-        output_filenames.split_dwarf_path(tcx.sess.split_debuginfo(), Some(codegen_unit_name)).map(
-            |f| {
-                let joined = out_dir.join(f);
-                tcx.sess.source_map().path_mapping().map_prefix(joined).0
-            },
-        )
+        output_filenames
+            .split_dwarf_path(tcx.sess.split_debuginfo(), Some(codegen_unit_name))
+            // We get a path relative to the working directory from split_dwarf_path
+            .map(|f| tcx.sess.source_map().path_mapping().map_prefix(f).0)
     } else {
         None
     }