FreeBSD `fts.c`, 05d8276 on Feb 10, 2013 (https://github.com/lattera/freebsd/)

Really hacky port. Sorry.

Don't forget to include Library/FTSLib.h instead of fts.h.

Limitations (mostly of edk2 StdLib implementation):

FTS_NOCHDIR is forced (no fchdir)
No smartness around avoiding extra stat calls (no st_nlink)
No st_dev, st_ino (no cycle detection, among other things)
No graceful dealing with non-ASCII file names (d_name is wide).