Implement `truncate`, fix `mkfifo` on linux and add tests
- Implement truncate based upon ftruncate.
- Make sure to pass
S_IFIFOwhen calling mkfifo on linux
- Contain the unsafe block to reading a the raw pointer in
- Add tests to check for regression. Since FIFOs are not supported on Redox, don't add the mkfifo test to the permanent testsuite