Move linux qsort def to platform header

Moving qsort to the platform header allows each platform to
provide an appropriate sorting implementation.

Reviewed-by: Allan Jude <allanjude@freebsd.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #9663

module/zcommon/zprop_common.c

@@ -41,11 +41,7 @@
 #include "zfs_prop.h"
 #include "zfs_deleg.h"
 
-#if defined(_KERNEL)
-#include <linux/sort.h>
-#define	qsort(base, num, size, cmp) \
-    sort(base, num, size, cmp, NULL)
-#else
+#if !defined(_KERNEL)
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>