[Ada] Gigi support for OpenACC pragmas

[Ada] Gigi support for OpenACC pragmas

Matching front-end bits to support Acc_Kernels, Acc_Parallel,
Acc_Loop and Acc_Data.

2018-12-03  Olivier Hainque  <hainque@adacore.com>

gcc/ada/

	* gcc-interface/lang.opt (fopenacc): New option for Ada.
	* gcc-interface/misc.c (gnat_handle_option): Handle it.
	* gcc-interface/trans.c (struct loop_info_d): Add OMP
	attributes.
	(Iterate_Acc_Clause_Arg, Acc_gnat_to_gnu): New functions,
	helpers for OpenACC pragmas processing in Pragma_to_gnu.
	(Acc_Var_to_gnu, Acc_Reduc_Var_to_gnu, Acc_Reduc_to_gnu):
	Likewise.
	(Acc_Size_Expr_to_gnu, Acc_Size_List_to_gnu): Likewise.
	(Pragma_Acc_Data_to_gnu): Likewise.
	(Pragma_to_gnu): Handle Pragma_Acc_Loop, Pragma_Acc_Data,
	Pragma_Acc_Kernels and Pragma_Acc_Parallel.
	(Acc_Loop_to_gnu, Regular_Loop_to_gnu): New functions. Helpers
	for ...
	(Loop_Statement_to_gnu): Rework to handle OpenACC loops.

From-SVN: r266748