* common.opt: Add -Wattribute-warning.
         * doc/invoke.texi: Add documentation for -Wno-attribute-warning.
         * expr.c (expand_expr_real_1): Add new attribute to warning_at
         call to allow user configure behavior of "warning" attribute.

         * gcc.dg/Wno-attribute-warning.c: New test.

From-SVN: r265891