fchflags(2) on macOS

The text 8a63c5341898, as OS X 10.11.6, OS X 10.11.5, OS X 10.11.4, OS X 10.11.3, OS X 10.11.2, OS X 10.11.1, OS X 10.11 shipped it.

set file flags

fchflags(2) on macOS now