apparmor: fix zero-length compiler warning in AA_BUG()

Uses of AA_BUG() without a message can result in the compiler warning

  warning: zero-length gnu_printf format string [-Wformat-zero-length]

Fix this with a pragma for now. A larger rework of AA_BUG() will
follow.

Signed-off-by: John Johansen <john.johansen@canonical.com>

Author: jrjohansen

security/apparmor/include/lib.h

@@ -31,7 +31,12 @@
 
 #define AA_WARN(X) WARN((X), "APPARMOR WARN %s: %s\n", __func__, #X)
 
-#define AA_BUG(X, args...) AA_BUG_FMT((X), "" args)
+#define AA_BUG(X, args...)						    \
+	do {								    \
+		_Pragma("GCC diagnostic ignored \"-Wformat-zero-length\""); \
+		AA_BUG_FMT((X), "" args);				    \
+		_Pragma("GCC diagnostic warning \"-Wformat-zero-length\""); \
+	} while (0)
 #ifdef CONFIG_SECURITY_APPARMOR_DEBUG_ASSERTS
 #define AA_BUG_FMT(X, fmt, args...)					\
 	WARN((X), "AppArmor WARN %s: (" #X "): " fmt, __func__, ##args)