audit: avoid -Wempty-body warning

gcc warns about an empty statement when audit_remove_mark is defined to
nothing:

kernel/auditfilter.c: In function 'audit_data_to_entry':
kernel/auditfilter.c:609:51: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
  609 |                 audit_remove_mark(entry->rule.exe); /* that's the template one */
      |                                                   ^

Change the macros to use the usual "do { } while (0)" instead, and change a
few more that were (void)0, for consistency.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit.h

@@ -292,8 +292,8 @@ extern void audit_filter_inodes(struct task_struct *tsk,
 extern struct list_head *audit_killed_trees(void);
 #else /* CONFIG_AUDITSYSCALL */
 #define auditsc_get_stamp(c, t, s) 0
-#define audit_put_watch(w) {}
-#define audit_get_watch(w) {}
+#define audit_put_watch(w) do { } while (0)
+#define audit_get_watch(w) do { } while (0)
 #define audit_to_watch(k, p, l, o) (-EINVAL)
 #define audit_add_watch(k, l) (-EINVAL)
 #define audit_remove_watch_rule(k) BUG()
@@ -302,8 +302,8 @@ extern struct list_head *audit_killed_trees(void);
 
 #define audit_alloc_mark(k, p, l) (ERR_PTR(-EINVAL))
 #define audit_mark_path(m) ""
-#define audit_remove_mark(m)
-#define audit_remove_mark_rule(k)
+#define audit_remove_mark(m) do { } while (0)
+#define audit_remove_mark_rule(k) do { } while (0)
 #define audit_mark_compare(m, i, d) 0
 #define audit_exe_compare(t, m) (-EINVAL)
 #define audit_dupe_exe(n, o) (-EINVAL)
@@ -311,8 +311,8 @@ extern struct list_head *audit_killed_trees(void);
 #define audit_remove_tree_rule(rule) BUG()
 #define audit_add_tree_rule(rule) -EINVAL
 #define audit_make_tree(rule, str, op) -EINVAL
-#define audit_trim_trees() (void)0
-#define audit_put_tree(tree) (void)0
+#define audit_trim_trees() do { } while (0)
+#define audit_put_tree(tree) do { } while (0)
 #define audit_tag_tree(old, new) -EINVAL
 #define audit_tree_path(rule) ""	/* never called */
 #define audit_kill_trees(context) BUG()