libfixposix: 0.4.1 -> 0.4.3

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 0.4.3 with grep in /nix/store/ksrz74w4gzxb2mf8yb3f3i67i80cr93v-libfixposix-0.4.3
- directory tree listing: https://gist.github.com/ddc89b6def68fbc70c046bfdaa1c02b8