lib/attr.h: Add ATTR_STRING() attribute macro

It signals that a function parameter is a string _before_ the call.

Suggested-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/attr.h

@@ -21,5 +21,11 @@
 # define ATTR_MALLOC(deallocator)
 #endif
 
+#if (__GNUC__ >= 14)
+# define ATTR_STRING(...)       [[gnu::null_terminated_string_arg(__VA_ARGS__)]]
+#else
+# define ATTR_STRING(...)
+#endif
+
 
 #endif  // include guard