Compilation: unrevert some stuff

Author: andrewrk

src/Compilation.zig

@@ -998,13 +998,13 @@ pub const CObject = struct {
 
                 const file = fs.cwd().openFile(file_name, .{}) catch break :source_line 0;
                 defer file.close();
-                file.seekTo(diag.src_loc.offset + 1 - diag.src_loc.column) catch break :source_line 0;
-
-                var line = std.ArrayList(u8).init(eb.gpa);
-                defer line.deinit();
-                file.deprecatedReader().readUntilDelimiterArrayList(&line, '\n', 1 << 10) catch break :source_line 0;
-
-                break :source_line try eb.addString(line.items);
+                var buffer: [1024]u8 = undefined;
+                var file_reader = file.reader(&buffer);
+                file_reader.seekTo(diag.src_loc.offset + 1 - diag.src_loc.column) catch break :source_line 0;
+                var aw: Writer.Allocating = .init(eb.gpa);
+                defer aw.deinit();
+                _ = file_reader.interface.streamDelimiterEnding(&aw.writer, '\n') catch break :source_line 0;
+                break :source_line try eb.addString(aw.getWritten());
             };
 
             return .{