[Bug c/80868] New: "Duplicate const" warning emitted in `const typeof(foo) bar;`

[george.burgess.iv at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80868

            Bug ID: 80868
           Summary: "Duplicate const" warning emitted in `const
                    typeof(foo) bar;`
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: george.burgess.iv at gmail dot com
  Target Milestone: ---

Minimal test-case (repros with 7.1: https://godbolt.org/g/A2dTCP):

$ cat tc.c
const int i;
const typeof(i) j;

$ gcc -std=gnu89 -pedantic tc.c
2:17: warning: duplicate 'const' [-Wpedantic]
 const typeof(i) j;

Expected behavior: no duplicate const warning when there's only one `const` on
the decl for `j`.

While the current behavior is understandable, I think it would be good to relax
the warning in this case. typeof is often used in macros, so silencing this
warning isn't always trivial. Since typeof is also a language extension, I
don't believe that C89 6.5.3 (which I assume is the only reason GCC is emitting
these complaints in the first place) needs to apply here.

Thank you for your time :)