Compiler Attributes: counted_by: Adjust name and identifier expansion

GCC and Clang's current RFCs name this attribute "counted_by", and have
moved away from using a string for the member name. Update the kernel's
macros to match. Additionally provide a UAPI no-op macro for UAPI structs
that will gain annotations.

Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Fixes: dd06e72e68 ("Compiler Attributes: Add __counted_by macro")
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20230817200558.never.077-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

include/uapi/linux/stddef.h

@@ -45,3 +45,7 @@
 		TYPE NAME[]; \
 	}
 #endif
+
+#ifndef __counted_by
+#define __counted_by(m)
+#endif