Use C_INT64_T from ISO_C_BINDING (to avoid using a Fortran 2008 feature) for...

Use C_INT64_T from ISO_C_BINDING (to avoid using a Fortran 2008 feature) for casting INT to INT64 in cdi_write_f2003.f90.

examples/cdi_write_f2003.f90

       PROGRAM CDIWRITEF2003
 
       USE iso_c_binding
-      USE iso_fortran_env, ONLY : int64
       USE mo_cdi
 
       IMPLICIT NONE
@@ -73,7 +72,7 @@
 !     Loop over the number of time steps
       DO tsID = 0, nts-1
 !        Set the verification date to 1985-01-01 + tsID
-         CALL taxisDefVdate(taxisID, 19850101_int64+tsID)
+         CALL taxisDefVdate(taxisID, 19850101_c_int64_t+tsID)
 !        Set the verification time to 12:00:00
          CALL taxisDefVtime(taxisID, 120000)
 !        Define the time step