Is [[nodiscard]] any different from [[gnu::warn_unused_result]]?

I had some code that used the GCC extension [[gnu::warn_unused_result]] (a.k.a. __attribute__((__warn_unused_result__))). Now I attempted to use C2x's [[nodiscard]] and I got an incomprehensible error. I'm not sure if the usage of [[nodiscard]] is considerably different from the old GCC attribute, or if it's just a bug in GCC:

$ cat warn_unused_result.c [[gnu::warn_unused_result]]int foo(void);[[gnu::warn_unused_result]]int bar(void);int foo(void){    return 1;}int bar(void){    return foo();}

$ cc -Wall -Wextra -Werror -std=c2x -c warn_unused_result.c

$ cat nodiscard.c [[nodiscard]]int foo(void);[[nodiscard]]int bar(void);int foo(void){    return 1;}int bar(void){    return foo();}

$ cc -Wall -Wextra -Werror -std=c2x -c nodiscard.c          nodiscard.c:2:1: error: 'nodiscard' attribute directive ignored [-Werror=attributes]    2 | int foo(void);      | ^~~nodiscard.c:5:1: error: 'nodiscard' attribute directive ignored [-Werror=attributes]    5 | int bar(void);      | ^~~cc1: all warnings being treated as errors

$ cc --versioncc (Debian 10.2.1-6) 10.2.1 20210110Copyright (C) 2020 Free Software Foundation, Inc.This is free software; see the source for copying conditions.  There is NOwarranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Obviously, I'm not ignoring the return value of any of the functions.

That 1 is never lost (the callers of bar() are in a different translation unit, which might be the problem triggering GCC's behavior?...)