self hosted compiler: avoid Dir.realpathAlloc

The use of Dir-related realpath functions will put std.os.getFdPath in
the critical path which makes the compiler less portable.

src/Compilation.zig

@@ -4074,7 +4074,14 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: *std.P
                 args_dir, args_hex_hash[0..],
             });
             try output_dir.handle.writeFile(args_file, args);
-            const args_file_path = try output_dir.handle.realpathAlloc(allocator, args_file);
+
+            const args_file_path = args_file_path: {
+                if (output_dir.path) |odp| {
+                    break :args_file_path try fs.path.join(allocator, &[_][]const u8{ odp, args_file });
+                } else {
+                    break :args_file_path args_file;
+                }
+            };
 
             argv.shrinkRetainingCapacity(2);
             try argv.append(try std.mem.concat(allocator, u8, &[_][]const u8{ "@", args_file_path }));