trans.c (gigi): Do not start statement group.

	* gcc-interface/trans.c (gigi): Do not start statement group.
	(Compilation_Unit_to_gnu): Set current_function_decl to NULL.
	Start statement group and push binding level here...
	(gnat_to_gnu) <N_Compilation_Unit>: ...and not here.
	Do not push fake contexts at top level.  Remove redundant code.
	(call_to_gnu): Rename a local variable and constify another.
	* gcc-interface/utils.c (gnat_pushlevel): Fix formatting nits.
	(set_current_block_context): Set it as the group's block.
	(gnat_init_decl_processing): Delete unrelated init code.
	(end_subprog_body): Use NULL_TREE.

From-SVN: r158370