[Bug c/71613] New: Useful warnings silenced when macros from system headers are used

[ch3root at openwall dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71613

            Bug ID: 71613
           Summary: Useful warnings silenced when macros from system
                    headers are used
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ch3root at openwall dot com
  Target Milestone: ---

Useful warnings seem to be silenced when macros from system headers are used.
For example, in the example below a warning would be useful for both enums but
only one warning is shown. The same can probably happen for other warnings.

Source code:

----------------------------------------------------------------------
#include <limits.h>

int main()
{
  enum { e1 = LLONG_MIN };
  enum { e2 = +LLONG_MIN };
}
----------------------------------------------------------------------

Results:

----------------------------------------------------------------------
$ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out
test.c: In function ‘main’:
test.c:6:15: warning: ISO C restricts enumerator values to range of ‘int’
[-Wpedantic]
   enum { e2 = +LLONG_MIN };
               ^
----------------------------------------------------------------------

gcc version: gcc (GCC) 7.0.0 20160616 (experimental)