https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100939
--- Comment #1 from johnfbennett at protonmail dot com ---
G++ does have a good warning for this scenario:
$ g++ -Wall misplacedattribute.c
misplacedattribute.c: In function ‘int main()’:
misplacedattribute.c:7:37: warning: attributes ignored on
elaborated-type-specifier that is not a forward declaration [-Wattributes]
7 | struct __attribute__((__unused__)) samplestruct samplestruct;
| ^~~~~~~~~~~~
misplacedattribute.c:7:50: warning: unused variable ‘samplestruct’
[-Wunused-variable]
7 | struct __attribute__((__unused__)) samplestruct samplestruct;
| ^~~~~~~~~~~~
