Breaking change in nix 0.26.3 due to bitflags upgrade

[ogoffart]

In nix 0.26.3, the bitflags crate was updated which is technically a breaking change.
For example, the function nix::fcntl::OFlag::from_bits_unchecked no longer exist.

(Note: while we were using that function in our project, we're going to port to 0.27 anyway so we're not going to be impacted by this change, but i just wanted to report the issue just in case you think this is worth fixing. I can suggest either reverting the change, or add the missing functions in libc_bitflags macro. )

[ogoffart]

we're not going to be impacted by this change

Actually, i spoke too soon, one of my dependencies from crates.io (calloop) is impacted

error[E0599]: no function or associated item named `from_bits_unchecked` found for struct `OFlag` in the current scope
  --> ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/calloop-0.11.0/src/io.rs:55:41
   |
55 |         let old_flags = unsafe { OFlag::from_bits_unchecked(old_flags) };
   |                                         ^^^^^^^^^^^^^^^^^^^ function or associated item not found in `OFlag`

In light of that, i believe something should be done about it. (and 0.26.3 should probably be yanked)

[asomers]

Fixed by #2117 .