* 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.
* testsuite/gcc.dg/format/null-1.c: New test.

From-SVN: r53801