Add string format checking to err.h functions

And fix all problems this detected... oops

include/helpers.h

@@ -11,11 +11,14 @@
 
 #ifdef __GNUC__
 	/* GCC or compatible */
+	#define format_(archetype, str_index, first_arg) \
+		__attribute__ ((format (archetype, str_index, first_arg)))
 	#define noreturn_	__attribute__ ((noreturn))
 	#define unused_		__attribute__ ((unused))
 	#define trap_		__builtin_trap()
 #else
 	/* Unsupported, but no need to throw a fit */
+	#define format_(archetype, str_index, first_arg)
 	#define noreturn_
 	#define unused_
 	#define trap_