Silence clang warning of flexible array not at end

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Youzhong Yang <yyang@mathworks.com>
Closes openzfs#14764

include/sys/dmu_objset.h

@@ -72,6 +72,10 @@ struct dmu_tx;
  */
 #define	OBJSET_CRYPT_PORTABLE_FLAGS_MASK	(0)
 
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wgnu-variable-sized-type-not-at-end"
+#endif
 typedef struct objset_phys {
 	dnode_phys_t os_meta_dnode;
 	zil_header_t os_zil_header;
@@ -88,6 +92,9 @@ typedef struct objset_phys {
 	char os_pad1[OBJSET_PHYS_SIZE_V3 - OBJSET_PHYS_SIZE_V2 -
 	    sizeof (dnode_phys_t)];
 } objset_phys_t;
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
 
 typedef int (*dmu_objset_upgrade_cb_t)(objset_t *);