c++/9367: [3.3/3.4 regression] error: nonnull argument with extern "C" snprintf prototype

[Janis Johnson]

The regression showed up with this patch:

2002-05-23  Jason Thorpe  <thorpej@wasabisystems.com>

      * builtin-attrs.def: Update copyright years.
      (ATTR_NONNULL): New attribute identifier.
      (ATTR_NONNULL_1, ATTR_NONNULL_2, ATTR_NONNULL_3): New
      attribute tree lists.
      (DEF_FORMAT_ATTRIBUTE): Chain a nonnull attribute for the
      format operand.
      (ATTR_FORMAT_ARG_1, ATTR_FORMAT_ARG_2): Use...
      (DEF_FORMAT_ARG_ATTRIBUTE): ...this to generate format_arg
      attribute lists.  Chain the appropriate nonnull attribute.
      * c-format.c (check_format_arg): Remove null format string
      warning.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9367