[Bug c/70883] inconsistent error message for calls to __builtin_add_overflow with too few arguments

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70883

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Standalone patch requested and posted here:
https://gcc.gnu.org/ml/gcc-patches/2016-06/msg00093.html