makefs: Fix issues building as a cross-tool on non-FreeBSD

This adds missing includes, uses the standard dirent.h rather than the
BSD-specific sys/dirent.h subset (which works on macOS but not Linux)
and works around Linux's lack of st_birthtim.

This allows usr.sbin/makefs to be added to LOCAL_XTOOL_DIRS again on
macOS and Linux so that disk images can be cross-built.

Reviewed by:	markj
Fixes:		240afd8c1f ("makefs: Add ZFS support")
Differential Revision:	https://reviews.freebsd.org/D36135

usr.sbin/makefs/zfs/dsl.c

@@ -29,6 +29,7 @@
  */
 
 #include <assert.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <util.h>

usr.sbin/makefs/zfs/fs.c

@@ -28,11 +28,12 @@
  * SUCH DAMAGE.
  */
 
-#include <sys/dirent.h>
 #include <sys/stat.h>
 
 #include <assert.h>
+#include <dirent.h>
 #include <fcntl.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -456,7 +457,12 @@ fs_populate_sattrs(struct fs_populate_arg *arg, const fsnode *cur,
 	fs_populate_time(fs, attrbuf, &sb->st_mtim, ZPL_ATIME, &bonussz);
 	fs_populate_time(fs, attrbuf, &sb->st_ctim, ZPL_CTIME, &bonussz);
 	fs_populate_time(fs, attrbuf, &sb->st_mtim, ZPL_MTIME, &bonussz);
+#ifdef __linux__
+	/* Linux has no st_birthtim; approximate with st_ctim */
+	fs_populate_time(fs, attrbuf, &sb->st_ctim, ZPL_CRTIME, &bonussz);
+#else
 	fs_populate_time(fs, attrbuf, &sb->st_birthtim, ZPL_CRTIME, &bonussz);
+#endif
 
 	fs_populate_varszattr(fs, attrbuf, aces, sizeof(aces), 0,
 	    ZPL_DACL_ACES, &bonussz);

usr.sbin/makefs/zfs/objset.c

@@ -29,6 +29,7 @@
  */
 
 #include <assert.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <util.h>

usr.sbin/makefs/zfs/vdev.c

@@ -30,6 +30,7 @@
 
 #include <assert.h>
 #include <fcntl.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 

usr.sbin/makefs/zfs/zap.c

@@ -33,6 +33,7 @@
 
 #include <assert.h>
 #include <stddef.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <util.h>

usr.sbin/makefs/zfs/zfs.h

@@ -32,6 +32,7 @@
 #define	_MAKEFS_ZFS_H_
 
 #include <sys/types.h>
+#include <sys/endian.h>
 #include <sys/queue.h>
 
 #include <bitstring.h>