Fix references declared in lexically-enclosing OpenACC data region

Fix references declared in lexically-enclosing OpenACC data region

	gcc/fortran/
	* trans-openmp.c (gfc_omp_finish_clause): Guard addition of clauses for
	pointers with DECL_P.

	gcc/
	* gimplify.c (oacc_array_mapping_info): Add REF field.
	(gimplify_scan_omp_clauses): Initialise above field for data blocks
	passed by reference.
	(gomp_oacc_needs_data_present): Handle references.
	(gimplify_adjust_omp_clauses_1): Handle references and optional
	arguments for variables declared in lexically-enclosing OpenACC data
	region.

(cherry picked from openacc-gcc-9-branch commit
a2ed98fb31686fcdbaa7bd1396de5c31567b3729)