[Bug c/67964] New: [4.9/5/6 Regression] Multiple attributes wrongly accepted without commas

["jsm28 at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67964

            Bug ID: 67964
           Summary: [4.9/5/6 Regression] Multiple attributes wrongly
                    accepted without commas
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jsm28 at gcc dot gnu.org
  Target Milestone: ---

GCC wrongly accepts:

extern int foo (void) __attribute__ ((const const));

Multiple attributes inside a single __attribute__ (()) should be required to be
separated by commas, so ((const, const)).  Bug introduced in 4.1 with the new C
parser.