Fortran/OpenMP: Fix declare_variant's 'adjust_args' mishandling with return by refere...

Fortran/OpenMP: Fix declare_variant's 'adjust_args' mishandling with return by reference [PR118321]

declare_variant's 'adjust_args' clause references the arguments in the
middle end by the argument position; this has to account for hidden
arguments that are inserted before due to return by reference,
as done in this commit.

	PR fortran/118321

gcc/fortran/ChangeLog:

	* trans-openmp.cc (gfc_trans_omp_declare_variant): Honor hidden
	arguments for append_arg's need_device_ptr.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/adjust-args-12.f90: New test.