Add Haiku support.

This replaces the use of a few BSD-specific functions, as well
as the direct references to _open/_close et-al.

BFS doesn't support the FTS_NOSTAT directory link count optimization,
and no statfs() function is available, so we simply turn that off.

headers/posix/fts.h

@@ -33,6 +33,8 @@
 #ifndef	_FTS_H_
 #define	_FTS_H_
 
+#include <sys/cdefs.h>
+
 typedef struct {
 	struct _ftsent *fts_cur;	/* current node */
 	struct _ftsent *fts_child;	/* linked list of children */
@@ -52,7 +54,6 @@ typedef struct {
 #define	FTS_PHYSICAL	0x010		/* physical walk */
 #define	FTS_SEEDOT	0x020		/* return dot and dot-dot */
 #define	FTS_XDEV	0x040		/* don't cross devices */
-#define	FTS_WHITEOUT	0x080		/* return whiteout information */
 #define	FTS_OPTIONMASK	0x0ff		/* valid user option mask */
 
 #define	FTS_NAMEONLY	0x100		/* (private) child names only */

headers/posix/ftw.h

@@ -25,6 +25,7 @@
 #ifndef	_FTW_H
 #define	_FTW_H
 
+#include <sys/cdefs.h>
 #include <sys/types.h>
 #include <sys/stat.h>