coff: add missing Dll.zig source file

src/Coff/Dll.zig

@@ -0,0 +1,47 @@
+path: []const u8,
+index: File.Index,
+
+alive: bool = false,
+
+pub fn deinit(self: *Dll, allocator: Allocator) void {
+    allocator.free(self.path);
+}
+
+pub fn addExport(self: *Dll, coff_file: *Coff, args: struct {
+    name: [:0]const u8,
+    type: coff.ImportType,
+    name_type: coff.ImportNameType,
+    hint: u16,
+}) !void {
+    _ = self;
+    _ = coff_file;
+    log.debug("TODO: add symbol '{s}' of type {s}, name_type {s} and hint {x}", .{
+        args.name,
+        @tagName(args.type),
+        @tagName(args.name_type),
+        args.hint,
+    });
+}
+
+pub fn format(
+    self: *Dll,
+    comptime unused_fmt_string: []const u8,
+    options: std.fmt.FormatOptions,
+    writer: anytype,
+) !void {
+    _ = self;
+    _ = unused_fmt_string;
+    _ = options;
+    _ = writer;
+    @compileError("do not format Dll directly");
+}
+
+const coff = std.coff;
+const log = std.log.scoped(.coff);
+const mem = std.mem;
+const std = @import("std");
+
+const Allocator = mem.Allocator;
+const Coff = @import("../Coff.zig");
+const Dll = @This();
+const File = @import("file.zig").File;