[Bug c/63543] incomplete type error should suppress duplicates

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63543

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
The C++ FE prints:

test.c:6:12: error: invalid use of incomplete type ‘struct undefined’
   int x = f->a;
            ^
test.c:2:8: note: forward declaration of ‘struct undefined’
 struct undefined;
        ^

but it also prints it three times.