[libcxx] [test] Call create_directory_symlink when linking directories

[mstorsjo]

Summary

This makes the symlinks work properly on windows.

A similar round of cleanup was done in c41bda7f5fc26e4602a029646991d6a5c59cb365, but these tests were added after that.

[mstorsjo]

Rebased, retry CI.

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.create_directory/create_directory.pass.cpp

TEST_CASE(dest_part_is_file)
     TEST_CHECK(is_regular_file(file));
     TEST_CHECK(!exists(dir));
 }
 
 TEST_CASE(dest_is_symlink_to_dir)
 {
     scoped_test_env env;
     const path dir = env.create_dir("dir");
-    const path sym = env.create_symlink(dir, "sym_name");
+    const path sym = env.create_directory_symlink(dir, "sym_name");
     std::error_code ec = GetTestEC();
     TEST_CHECK(create_directory(sym, ec) == false);
     TEST_CHECK(!ec);
 }
 
 TEST_CASE(dest_is_symlink_to_file)
 {
     scoped_test_env env;
     const path file = env.create_file("file");
     const path sym = env.create_symlink(file, "sym_name");
     std::error_code ec = GetTestEC();
     TEST_CHECK(create_directory(sym, ec) == false);
     TEST_CHECK(ec);
 }
 
 TEST_SUITE_END()

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.create_directory/create_directory_with_attributes.pass.cpp

const path sym = env.create_symlink("dne_sym", "dne_sym_name");
     TEST_CHECK(create_directory(sym, attr_dir, ec) == false);
     TEST_CHECK(ec);
   }
 }
 
 TEST_CASE(dest_is_symlink_to_dir) {
   scoped_test_env env;
   const path dir = env.create_dir("dir");
-  const path sym = env.create_symlink(dir, "sym_name");
+  const path sym = env.create_directory_symlink(dir, "sym_name");
   const path attr_dir = env.create_dir("attr_dir");
   {
     std::error_code ec = GetTestEC();
     TEST_CHECK(create_directory(sym, attr_dir, ec) == false);
     TEST_CHECK(!ec);
   }
 }