Fortran 2018: An argument to an intrinsic procedure other than ASSOCIATED,
NULL, or PRESENT shall be a data object.  An EXPR_NULL is not a data
object.  Add checks for intrinsics.

2020-06-11  Steven G. Kargl  <kargl@gcc.gnu.org>
	    Harald Anlauf  <anlauf@gmx.de>

gcc/fortran/
	PR fortran/95544
	* check.c (invalid_null_arg): Rename to gfc_invalid_null_arg.
	(gfc_check_associated, gfc_check_kind, gfc_check_merge)
	(gfc_check_shape, gfc_check_size, gfc_check_spread)
	(gfc_check_transfer): Adjust.
	(gfc_check_len_lentrim, gfc_check_trim): Check for NULL() argument.
	* gfortran.h: Declare gfc_invalid_null_arg ().
	* intrinsic.c (check_arglist): Check for NULL() argument.

(cherry picked from commit 7fd614ee818983274eb5e47cbb8ec68b20994963)