Fix compiler warnings about zero-length arrays in inline bitops

The compiler appears to be expanding the unused NULL pointer into a
zero-length array via the inline bitops code. When -Werror=array-bounds
is used, this causes a build failure. Recommended solution is allocate
temporary structures, fill with zeros (to avoid uninitialized data use
warnings), and pass the pointer to those to the inline calls.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #13463 
Closes #13465

config/kernel-blk-queue.m4

@@ -93,8 +93,10 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE_DISCARD], [
 	ZFS_LINUX_TEST_SRC([blk_queue_discard], [
 		#include <linux/blkdev.h>
 	],[
-		struct request_queue *q __attribute__ ((unused)) = NULL;
+		struct request_queue r;
+		struct request_queue *q = &r;
 		int value __attribute__ ((unused));
+		memset(q, 0, sizeof(r));
 		value = blk_queue_discard(q);
 	])
 ])
@@ -119,16 +121,20 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE_SECURE_ERASE], [
 	ZFS_LINUX_TEST_SRC([blk_queue_secure_erase], [
 		#include <linux/blkdev.h>
 	],[
-		struct request_queue *q __attribute__ ((unused)) = NULL;
+		struct request_queue r;
+		struct request_queue *q = &r;
 		int value __attribute__ ((unused));
+		memset(q, 0, sizeof(r));
 		value = blk_queue_secure_erase(q);
 	])
 
 	ZFS_LINUX_TEST_SRC([blk_queue_secdiscard], [
 		#include <linux/blkdev.h>
 	],[
-		struct request_queue *q __attribute__ ((unused)) = NULL;
+		struct request_queue r;
+		struct request_queue *q = &r;
 		int value __attribute__ ((unused));
+		memset(q, 0, sizeof(r));
 		value = blk_queue_secdiscard(q);
 	])
 ])