zig: show list of files in a directory

A usage of list files, is building existed C libraries, listing all C files is annoying.

var general = std.heap.GeneralPurposeAllocator(.{}){};
defer _ = general.deinit();

const dir = "./src/";
var sources = std.fs.Dir.Iterator{
    .dir = try std.fs.cwd().openDir(dir, .{}),
    .seek = 0,
    .buf = [_]u8{0} ** 8192,
    .index = 0,
    .end_index = 0,
};
var src = try sources.next();
while (src != null) : (src = try sources.next()) {
    const file = try std.mem.concat(general.allocator(), u8, &[_][]const u8{
	dir,
	src.?.name,
    });
    lib.addCSourceFile(file, &flags);
}