[gfortran] Better error reporting for ATAN2

[Paul Brook]

> 2004-08-26  Tobias Schlueter  <tobias.schlueter@physik.uni-muenchen.de>
>
> 	* check.c (gfc_check_atan2): New function.
> 	* intrinsic.c (add_functions): Use gfc_check_atan2 for ATAN2
> 	* intrinsic.h (gfc_check_atan2): Add prototype.

Ok.

Paul