OpenMP] Fix use_device_… with absent optional arg

OpenMP] Fix use_device_… with absent optional arg

        gcc/fortran/
        * trans-openmp.c (gfc_omp_is_optional_argument,
        gfc_omp_check_optional_argument): Handle type(c_ptr),value which uses a
        hidden argument for the is-present check.

        gcc/
        * omp-low.c (lower_omp_target): For use_device_ptr/use_derice_addr
        and Fortran's optional arguments, unconditionally add the is-present
        condition before the libgomp call.

        libgomp/
        * testsuite/libgomp.fortran/use_device_ptr-optional-2.f90: Add
        'type(c_ptr), value' test case. Conditionally map the per-value
        passed arguments.

From-SVN: r279004