[libcxx] Test accessing a directory on windows that gives "access denied" errors

Fix handling of skip_permission_denied on windows; after converting
the return value of GetLastError() to a standard error_code, ec.value()
is in the standard errc range, not a native windows error code. This
was missed in 15618072.

The directory "C:\System Volume Information" does seem to exist and
have these properties on most relevant contempory setups.

Differential Revision: https://reviews.llvm.org/D98166