[libcxx] [test] Mark bits of fs.enum tests as libcpp specific

The individual enum values in copy_options and file_type aren't
specified in the standard.

The standard doesn't require fs::path::format to be a scoped enum.

Differential Revision: https://reviews.llvm.org/D89866

GitOrigin-RevId: 545fb7a71c0c7e73b1d40ba1263d603ac6b17968
3 files changed