PR fortran/95980 - ICE in get_unique_type_string, at fortran/class.c:485

PR fortran/95980 - ICE in get_unique_type_string, at fortran/class.c:485

In SELECT TYPE, the argument may be an incorrectly specified unlimited
CLASS variable.  Avoid NULL pointer dereferences for clean error
recovery.

gcc/fortran/
	PR fortran/95980
	* class.c (gfc_add_component_ref, gfc_build_class_symbol):
	Add checks for NULL pointer dereference.
	* primary.c (gfc_variable_attr): Likewise.
	* resolve.c (resolve_variable, resolve_assoc_var)
	(resolve_fl_var_and_proc, resolve_fl_variable_derived)
	(resolve_symbol): Likewise.

(cherry picked from commit 70c884a4b82733027ac0e2620d09169b177080d7)