PR c/70883 - inconsistent error message for calls to __builtin_add_overflow
  with too few arguments

gcc/c-family/ChangeLog:
2016-06-09  Martin Sebor  <msebor@redhat.com>

	PR c/70883
	* c-common.c (builtin_function_validate_nargs): Make text of error
	message consistent with others like it.

gcc/testsuite/ChangeLog:
2016-06-09  Martin Sebor  <msebor@redhat.com>

	PR c/70883
	* c-c++-common/builtin-arith-overflow-1.c: Adjust diagnostic text.
	* gcc.dg/builtin-constant_p-1.c: Same.
	* gcc.dg/builtins-error.c: Same.
	* gcc.dg/pr70859.c: Same.

From-SVN: r237268