libstdc++: Fix filesystem::remove_all for Windows [PR104161]

The recursive_directory_iterator::__erase member was failing for
Windows, because the entry._M_type value is always file_type::none
(because _Dir_base::advance doesn't populate it for Windows) and
top.unlink uses fs::remove which sets an error using the
system_category. That meant that ec.value() was a Windows error code and
not an errno value, so the comparisons to EPERM and EISDIR failed.
Instead of depending on a specific Windows error code for attempting to
remove a directory, just use directory_entry::refresh() to query the
type first. This doesn't avoid the TOCTTOU races with directory
symlinks, but we can't avoid them on Windows without openat and
unlinkat, and creating symlinks requires admin privs on Windows anyway.

This also fixes the fs::remove_all(const path&) overload, which was
supposed to use the same logic as the other overload, but I forgot to
change it before my previous commit.

libstdc++-v3/ChangeLog:

	PR libstdc++/104161
	* src/c++17/fs_dir.cc (fs::recursive_directory_iterator::__erase):
	[i_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Refresh entry._M_type member,
	instead of checking for errno values indicating a directory.
	* src/c++17/fs_ops.cc (fs::remove_all(const path&)): Use similar
	logic to non-throwing overload.
	(fs::remove_all(const path&, error_code&)): Add comments.
	* src/filesystem/ops-common.h: Likewise.

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