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/linux/compiler_attributes.h

@@ -94,6 +94,19 @@
 # define __copy(symbol)
 #endif
 
+/*
+ * Optional: only supported since gcc >= 14
+ * Optional: only supported since clang >= 18
+ *
+ *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
+ * clang: https://reviews.llvm.org/D148381
+ */
+#if __has_attribute(__counted_by__)
+# define __counted_by(member)		__attribute__((__counted_by__(member)))
+#else
+# define __counted_by(member)
+#endif
+
 /*
  * Optional: not supported by gcc
  * Optional: only supported since clang >= 14.0
@@ -129,19 +142,6 @@
 # define __designated_init
 #endif
 
-/*
- * Optional: only supported since gcc >= 14
- * Optional: only supported since clang >= 17
- *
- *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
- * clang: https://reviews.llvm.org/D148381
- */
-#if __has_attribute(__element_count__)
-# define __counted_by(member)		__attribute__((__element_count__(#member)))
-#else
-# define __counted_by(member)
-#endif
-
 /*
  * Optional: only supported since clang >= 14.0
  *

include/uapi/linux/stddef.h

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