This test cannot be compiled under Redox. PR #1098 attempted to disable
it for Redox, but actually disabled it everywhere. AFAICT, Cargo has no
syntax to conditionally enable a target, except based on features.
Instead, use conditional compilation within the test.
The libc_bitflags! macro was replaced with a non-recursive one supporting
only public structs. I could not figure out how to make the old macro work
with the upgrade, so I reworked part of the bitflags! macro directly to suit
our needs, much as the original recursive macro was made. There are no uses
of this macro for non-public structs, so this is not a problem for internal code.
