Fix build breakage with current rustc:
error: the crate `bitflags` is compiled with the panic strategy `abort` which is incompatible with this crate's strategy of `unwind` error: aborting due to previous error error: the crate `bitflags` is compiled with the panic strategy `abort` which is incompatible with this crate's strategy of `unwind` error: aborting due to previous error error: Could not compile `gleam`.
